Lol, i lost 4th gear as well. Just keep a watch on your tranny temps if you can. I cant get mine fixed until i come up with the money for it. it sucks, but well it happens on our old cars, especially when you start modding them.
What probably caused yours to go bad just like mine is the 4th gear clutch shaft, they are very weak and over time like to sheer off. May want to check out ZZPerformance for a hardened 4th gear clutch shaft. Along with a rebuild kit if you want to do it yourself, thats what im doing.
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2000 GTP: XP Cammed/Blown/Nitrous