SB Modifications

LSPDFR spawns police vehicles more than would be expected in a non-LSPDFR playthrough which is why it seems this only occurs with LSPDFR. LSPDFR also loads other game assets, which when combined with user-added modified vehicle models/textures cause additional stress for the engine.
 
Adding Main.PreloadAllModels = false only stops models being loaded at the start, they will eventually be loaded in throughout the playthrough. The setting only delays the inevitable if you have vehicle models/high quality textures that cause this issue with GTA V's engine. Resource Adjuster as UnknownBastion suggested may help.

Just to ride on the back of UnknownBasition and Cyan:

UnknownBasition & Cyan are 100% correct on this.  LSPDFR will typically spawn in police vehicles (more than likely the same type of vehicles you have currently installed) they spawn nearby, further away and then eventually come within play render view of your character.  Note that it can even be a few streets over.  Then Lord forbid you press a Panic Button!

Most are not aware of a Megabyte Hard limit imposed by Rockstar on vehicle model size.  Whether that be a yft or ytd type of file.   The consensus for the Megabyte hard limit imposed is fairly close to 25mb to 30mb, give or take a mb or so.   So you can probably guess the trend that most vehicle mod authors have been going with and that is 4k textures.  Because we all want those 40mb worth of  Police Computers, Radios, Starbucks Cups, Ticketbooks, and printers that you will never see, even in first person *sarcasm off*

I won't mention much more as UnknownBasition and Cyan covered great recommendation with the  GTA Resource Adjuster and take a good look at your car models sizes.  Focus on that ytd,  there is are ways to reduce those file sizes and vids out there that go through Step by Step on how to maintain top quality and still cut the ytd size in half. 

(Probably not advisable to self promo my vids here)  

Good luck!

I tried the GTA Resource Adjuster, so far so good, no texture loss, some FPS loss but that's not a big deal I can work with changing some settings for that. Oh the joys of getting all your stuff working the way you are used to after buying a new computer, I appreciate all the help

Awesome!
I was about to write I also found the fix.
Slightly different to yours, I moved the GTAVLauncher, PlayGTAV, and GTAVLanguageSelect from the vanilla version and put them in the old 2944 version. I left the old GTA5.exe there and everything is working as normal again.

So you downloaded a fancy 2015 Tahoe and installed it in the police3 slot, only to find that it rolls more than your eyes when your boss is talking to you.  Does your Silverado not drive like a truck should? or maybe your '15 Charger doesn't feel right.    There are a lot of options to choose from when deciding which handlingid you want to use for your car.  I've compiled a list of what I use for handling lines, and thus far, all have worked just fine.  For some of them, such as the Silverado and Expedition, someone else might of found a better handling, and if that's the case, please comment below letting me know what you're using and I'll give it a shot. 
 
Some people like to edit the handling.meta.  This is not a requirement, the handlingid is all you need to touch if you just want the basics.  Handling.meta is there for those who know a bit about modding and want to refine the handling lines to feel realistic.
 
For those that might be confused on what the handlingid is, it's one of the top lines in the vehicles.meta.
 
Here's an example:
 
<handlingId>police3</handlingId>  
All of these will be for police vehicles, I will not be covering modded civilian cars.  Also note that this topic really only applies to those who have modded their police fleet.
 
 
Crown Vic
 
police  
 
Dodge Charger
 
If 09-10 version, police2  If 2013+ version, buffalo2  
 
Ford Taurus, Chevrolet Caprice and Chevrolet Impala 
 
police3 (this is meant for smaller vehicles, such as the Impala) premier (this is an alternative for smaller vehicles, such as the Impala.  Use this if you don't like the way police3 feels)  fugitive (this is meant for bigger/heavier cars, such as the Taurus) felon (this is an alternative for bigger/heavier cars in case you don't like Fugitive)  
 
Ford Explorer 
 
gresley  
 
Chevrolet Tahoe 
 
baller baller2  
Ford Expedition
 
fbi2  
Chevrolet Silverado
 
sandking  
Dodge Durango
 
baller  
Dodge Challenger
 
gauntlet  
Ford Mustang
 
dominator  
Ford Fusion
 
tailgater (There is most likely a very better choice out there, I'm just not sure which would work)  
BMW motorcycle
 
policeb  
Ford F-150
 
sandking  
Ford F-350
 
sadler  sandking - may work for this as well, not confirmed  
Chevrolet Corvette
 
coquette  
Chevrolet Avalanche
 
sandking  
Chevrolet Camaro
 
gauntlet  
Nissan GTR
 
elegy  
Land Rover
 
baller  
Hearse
 
romero  
Dodge Polara
 
glendale

idk i'm glad to be surrounded by Germans and Austrians and have no flag Xd

Yea soo, i removed every single file from dlcpacks (only with exception of patchday's m and n files and gta stuff) and it's working now so im gonna go with elimination method and adding every single file back one by one

Hey there. I'm not sure if this is the right section to post this but it seemed the best fit. Apologies if not.

So I found a way to avoid and get rid of texture pop-ups (when you look around too fast and things can't load in time with your camera movement, the map disappears, for example). I realized this had to do with my modded vehicles but didn't want to restrict myself to only download cars that COULD MAYBE NOT bug out my whole game. This can also solve EUP's issue of not being able to load the outfits or loading very slowly. This has to do with the same issue, Memory Overload.

The video guide I created was a result of what @bikinichampagne suggested (link in the description). All I did was create a system that would allow people who frequently update their police fleet for LSPDFR (as it's my case) to downscale unnecessary vehicle textures in a repetitive and quick way. I mean, who needs a 4K game-stock carbine or a 4K dirt skin? To me doesn't make sense, even in FPS patrols. With this form of downscaling, I couldn't even notice differences. Little letters were still readable and HD as seen in video.

This way you can still play with HQ models and textures... Difference is, your vehicles won't surpass the 25MB hard limit. So you get a stable gameplay without the expense of quality.
Aim for 20MB per vehicle.

It worked for me and the evidence is in the video itself (that's why its 22 mins long but has a time table so you can jump to the section you want). If it didn't work for you, you either aren't downscaling enough textures or your PC just cant handle it. Sorry, cant do miracles. You might wanna update your PC if he starts talking about Vietnam war stories. I guess GTA 5 will be too much sand for him and no downscaling in the world will save you from this.

So, all the relevant details are in the video. I guess what I'm trying here is to teach people a good practice to optimize their vehicles. Also you won't need proprietary software for any of this.

THIS WILL NOT MEAN MORE FRAMES PER SECOND. It will stabilize your game, might get rid of some stutters but this isn't a method to solve your FPS issues. Regardless, try it and luckily you can prove me wrong.

VIDEO
 

All I know to do is make sure all other plugins are updated to there latest version. Is crashing in a game or loading screen?