Finally got out and went to a local shop that uses a dynojet. It's not a load bearing but inertia. We had a hell of a time trying to keep the truck from downshifting into 4th. I was only able to pull off one clean run in 5th w/o the downshift. I also did a full throttle pull from first all the way through 5th, numbers didn't change much.
The truck made 578/1128, so I can't complain. They also let me do the pulls in my truck while they ran the dyno brake which put me a little more at ease.
I did however get a P0297 code, vehicle overspeed once. Is that bad?