Customs Tracks PO problem

Okay so I FINALLY got Grand Prix 3 working in Windows 7. I can play with custom carshapes and GPEdit, GPXpatch the works.

BUT for some reason any and all custom tracks send the PO back up to insane levels like 300%-800%. Only custom tracks are doing this and it's driving me crazy. After getting the base game to work I can't believe I've run into the same problem but only for the custom tracks. Is it to do with compatibility maybe? not sure you can even change stuff like that for Track .dat files?

Anyway if anyone else has had this issue is there a fix? or am I stuck with just the vanilla tracks?

HW-specs?

intel i5
AMD Radeon 6570
8gb Ram
win 7 64bit

The worst part is just how random this is, which makes sorting out the problem a nightmare. 1 out of every 10 loads the game will run a custom track no problem at all. Then in the same load on another track it will run terribly. Sometimes even the vanilla tracks will randomly have crazy PO. The fact this thing is so random is driving me crazy, I just don't know how to solve something when it's not even consistent.

sure you have ATI-systemtray together with your AMD Radeon. Try to make a preset for the game and disable all features like Antialiasing and other postproduction features. Set everything as fast as possible there!