FYI
a good stock rebuilt tranny with a couple internal updates and a new VB from suncoast will hold up to 700+ tq and over 300hp.
I just got the 47RE rebuilt in my '96. The builder works at a dealer in lake perris. He did a factory rebuild and took it back to brand new, with a few small updates like certain seals and stuff. Then I put it back together with a brand new suncoast Valve body. For a TC I picked up a PDQ HD diesel tranny converter only cost about $500. It has a extra low stall, billit cover and extra wide heavy duty clutch.
I'm pushing 311hp and 730tq and it locks up solid in all gears. I drop the truck into OD at 40mph, lock the TC and stand on the throttle. by 45mph the boost comes up to 34psi at about 1400rpm's and the joyride begins. 45-80 in about 5 seconds in a 7000# truck is a lot of fun.
My builder built the same tranny's for Freedom Diesels in Hemet but with his own VB. oh and the VB from SC came with the aluminum acumulator piston, billet anchor and 2nd gear apply strut.
So yeah, a stock built tranny can hold up with the right VB. the VB and converter are the most critical.
$1500 for that is a good deal.