Continuously random gangs shooting at me in vehicles while on duty. Followed the steps of installing the plugin and did it all correctly.

Did you use the search button before posting? You'd be surprised how many times this has been answered already! It's not an issue with LSPDFR. It's either a) conflicting plugin/script or b) you're at the part in the story where Michael and Trevor is banned from LS City limits. Progress further through the story or load an earlier save to solve this "issue".