Raven, my friend and fellow GTR2 B-Spec series organizer, I know pretty much the same situation just too well.
For the past, well I guess it's about two months by now, I've tried every possible solution I could think of to even out the three cars I'm dealing with, and every time it's felt like one step forward and ten steps back.
I just took myself the freedom to do a test run with my own, homemade AI drivers, and I too am having the Saleen about 1.5 seconds faster on Bathurst. That's not random, and it seems to me like the Saleen is just slightly better at mountaineering. Most of all this reminds me of our very own BMWs - half a season in, they're no longer dominating qualifying, but they're still subscribed to race wins.
Moral of the story is that as long as we're running cars that are actually different beyond a few stickers front and back, it'll never be perfectly equal. It can get close, but never dead-on. That, and our lovely AI isn't helping the spec testing at all
As for the graphical glitches and things, if there is a problem, feel free to send it to me. I might not always have the cure for the ebola ready in five minutes, nor will my parents always agree that being on the PC outside education-related things are a good idea, but if I see a gap in which to get things done, I will use the 🤬 out of it.
No matter what you do, don't pull the plug. You've come way too far for that. I felt like pulling the plug after S1, seeing as how many people in these B-Spec series' are afraid of creating what's essentially an avatar that has to worry about braking for a right-hander, but the few that are actually interested, on my opinion, far outweigh those other guys.
We are the few. The proud.
(and yes, I had to sneak in a reference to your livery. Deal with it )