That's a lot of torque on that tranny. Mine is just a little 5.4l gasser that's been beat ro crap over the years.I had an E350 Quigley 10' mini cube with a 4R100 and 7.3 Powerstroke and pulled a 7000lb GVW tandem axle trailer behind it up and down over very hilly terrain. That power train really had to work. Kept the oil clean It went 462,000 before it went. No sense trying to rebuild it. Put in a factory reman.