I want to baseline my new LLY before I start with the mods. Having a late model performance shop we deal with quite a few electronically shifted automatics (4L60E/4L80E). When on the dyno we are able to pull the motor and stay in one gear by using a special controller box that will keep the tranny at a 1:1 ratio which is typically where the dyno is measuring from. What do you do with the Allisons?? If you don't use a tranny controller box the transmission will down shift upon a load.

Any of the forum performance shops have a dyno and the trick to doing this?

Thanks

You will need a GM Tech 2 to command the tranny to stay in 4th gear.

Push the T/H and hold it to lock out 5th.
Get the truck to ~45mph, and roll into it.

Or get a Tech II

Pat,

I forgot that the T/H mode helps resist down shifts! The overdrive delete takes care of one gear at least!:cool2: