Already called the builder just trying to get some idea's because he will fix it on my coin because with 20,000 miles it is out of warranity.
I’ll assume it is an overdrive trans.
Take the truck for a ride in manual low gear, accel up to about 3500 then tip out of the throttle and see if you have engine braking.
Do it again in manual second and see if you have engine braking.
Report back.
PS - just my opinion, you should take it somewhere else if he is going to charge you without knowing what is wrong.
Most good rebuilders warranty their work past 20,000 miles.
