REDROVER
Explorer
My 6.2 was a J code with 160hp and 300lbs ft, it was in a 3/4 ton 2wd suburban and I never had heating issues unless I was really pushing it with a load up the mountains and then all I had to do was gear down and back off a bit on the speed. My current GM diesel is a 6.5TD heavy duty (I forget the code letter) and it seems ok to as long as I keep things within reason. I suspect you have an air flow issue, I have a friend that has a 6.5NA in a 110 with a custom rad and he doesn't have any heat problems. He is using a mechanical fan with ducting to make sure that it is drawing through the rad.
6.5 turbo in a hummer.u can push that truck to any hill and water never passes center line. but that radiator is huge.
the bottom line is we need air flow air flow and air flow,