Allison Transmission upgrades

I would contact a mechanic you trust, they should have some suggestions of what they have done.

That's the problem... I don't trust anyone here... that's why I"m asking here

if your transmission is slipping then it may need a service. Any triple disc billet torque converter would be a good choice for a slightly modified engine. if you have over 500hp then you probably want a 5 disc torque converter. new valve body and a shift kit could also help your transmission out. companies like ATS and BD make strong reliable torque converters. they also make super strong fully rebuilt transmissions.

I have had to replace the shifter switch at the transmission once and I know a friend that had to replace his as well, so I would replace it first. I lost 5th gear altogether and had erratic shifting in other gears. The trans is electricly controlled so any failure of that switch can cause all kinds of weirdness. It seems that the switch is the weak link in the Allison.