Ok firstly before you do anything else do this; go to your Playerdata folder and backup your Player.json (either move or rename to player.bak), then load the game and it will create a fresh player.json file.
Once you've done that race against the AI again, see if there's any difference, if there is and they're better could you please send me both your backup and fresh files?
As for your points;
- AI is erratic: Can't say I've noticed that behaviour myself, would need to see some video evidence.
- AI overtaking moves: Again hard to judge without video evidence, try lowering the Aggression setting to see if that "helps"
- AI with each other: Yeah that sounds like a mod/track issue, very rare that I've seen AI drop out that much during a race.
- AI at Sebring: I've had many many races at this track with the GT3 amongst others, never experienced any major issues at all and had some fantastic battles with the AI. Without knowing the guys settings in the video it could be his own fault not that of the game.
You may notice a trend to my points above "video evidence", if the player.json suggestion doesn't work (please try that first) then if possible take some video of the issues so it can be judged accordingly.
Over the years I've seen so many people claim to have AI problems and that they suck, only for them to never bring forward actual evidence or when they do it's clearly their driving style! It has to be viewed like a Race Steward at a real race meeting, whilst written text can point to some issues a video showing the AI is above all the best thing to see. I'm not saying you're at fault by the way (there may well be an issue), just that it's hard to say either way without seeing it for myself, especially as the issues you've stated above could be for any number of reasons.
I've not raced those cars on those tracks you've listed so cant comment on them specifically at this time.
Should the player.json change not work and you can't post a video, please post the exact AI settings you're using in game a long with exact weather conditions and RealRoad settings - which reminds me, the AI like rubber on the track just like us humans so on a Green track they may have a few moments just like we would!
Thanks