I have a 6.5 TD/4L80E truck that has 180k on the clock. It has been very reliable for me...once I learned about the PMD problem. the Pump Mounted Driver is a pair of high current transistors that control the electronic fuel injection pump. When it starts to go, the truck will stall repeatedly or not run at all. The trouble codes indicate thet the injector pump need to be replaced which is very high dollar and that solves the problem because the PMD is replaced at the same time. However, with the help of forums on these trucks, you learn to only replace the PMD and relocate it to a cooler place. Relatively cheap and easy to do. My favorite forum for these is
http://www.sixfiveturbodiesel.com/ .
I frequently haul an overhead camper and tow a boat or cars some distance without issues. The truck just loves to pull stuff at about 65 mph. Go faster and mileage drops off. I do alot of trailing with friends, sometimes involving 80 to 100 vehicles. Some of these guys nicknamed my truck "The Savior" because it doesn't fail and freqently is required to help them along.
This is the same engine/tranny in huge numbers of H1's serving in Iraq/Afganistan, hauling around the heft of up-armor. That indicates a relatively good track record and provides huge stockpiles of spare parts. The 6.2's were in military blazers and trucks before the H1's.
I think any of the options you are considering will require familiarizing yourself with the shortcomings of the drivetrain and being prepared to deal with them up front.
BTY a friend picked up a wrecked Penske truck at auction. He paid a little over 3K for a truck with a Cat engine (25k miles) and Allison auto tranny. He wound up removing the box and installing a 5th wheel for towing his toyhauler. He has less than $10K in it including all repairs, paint, etc.