TF 904 Auto slipping 2nd to 3rd when manual shifting @ higher revs

Cuda,
I can see why people do it with the 727/904 trans. [ leave the linkage off ] Once the engine is modified, it can be a lot of messing around to get the linkage/ratio just right for part throttle shifting and the WOT shift. The GM Turbo 400 system is much better.