Goin' through a 904

I don't know 904's well like 727's but I've heard they should have no problem standing up to anything up to 350 hp stock. I would still put in a Trans-go TF-2 kit just to eliminate any overlap and make it shift better. I think just doing this you should be fine.

Have you drove your GTX to see if it has all 3 forward gears working? If all the forward gears work it is a rear band/servo problem. If you don't have 3rd gear and reverse it's the front clutches. About the only way it will be an easy fix is if it's a rear servo problem. Anything else and the trans. has to come apart.