Transmission doesnt seam right
 

I have a lbz with a juice with attitude I've been noticing for a few years that when I'm on level 5 i seem to beable to make it rev up in which seams to be when it's in what I think is 4th gear it feels like the rpms climb faster then the speed does I'm not sure if its slipping or not it's not like the truck shutters or anything it's just seams like it revs up and doesn't pick speed up as fast as it should . I could be wrong about it being in 4th could be a different gear but it always happens at around 70-80 ish kmh doesnt mater if I have the programmer in or not or what it's set on . I have noticed every gear seams solid with it in th mode . It does it even after a fresh tranny service .

Other mods include 5" catback and egr blocker and finger stick 6" lift 33" tires kms 250000

I am no tranny expert but I believe the Allison will shut down if it senses slippage and also throw a CEL. This is the experience with the ex-SIL 2001 Duramax. When he has his tune turned up and steps into it to pass another vehicle his trans will go into neutral and he has to pull onto the shoulder and delete the fault code to get the truck to move. I could be wrong though.