Phienyxx

I don't think you need to uninstall Radiance V.  The only file is the visualsettings file.  On Realistic Radiance there is a visualsettings file that you will have to put in to replace with openIV.  Since it is a replacement you don't need to delete the first RadV visualsettings file.  Just install the Realistic Rad visualsettings and it will replace the file. 

Don’t give the Suspect the chance to run ? 😂 
 
jks You can do it on the Trainer mod menu

I've never experienced running out of breath, this is because I am pretty far along in the vanilla story mode I guess?  If so, maybe just take a hour or so (don't know how long it takes) to train your stamina to max? Otherwise StopThePed has a sprintboost feature that could work 

How do I artificially increase my characters stamina so I am not running out of breath and collapsing while I'm chasing a suspect? Is there a way to do this without going into the base game and increasing it normally?

The way I do it is to cuff the suspect and walk to your car then press E to open your door, then press E to make the suspect go inside your car.