i have recently installed a new 4spd tranny (t18) on my 1996 f250 went to drive it and it shifts fine but has no power goes good untill about 2000 rpm then it holds back and the rpms wont get any higher. when i installed it i did a new flywheel and clutch if that helps any. any help is appreciated

me thinks you have a computer problem with the engine.

It's pretty difficult to screw up a T-18 and I can't think of a scenario that would give you the results you are describing for a transmission malfunction.

the tranny i took out which was a c6 had a vacuum line on it if that is not being used now would that mess something up. the truck bogs down also if it is in neutral. i checked fule pressure and it is at 31 idling and 40 under a load

Flywheel.... Check the tooth count on the old one vs. the new one. What engine you got?

so you took the C-6 vacuum line off. Did you plug the hose or block it off at the manifold? If not you have a nice vacuum leak now.