Transmission is jacked...need suggestions

[Mr-Jack]

So this is on my 01' Chevy 2500 HD 4x4 6.0 w/4L80E. (Lifted on 35's w/4.10s...I know...need lower gears)

I mainly use the truck for hauling hay and every now and then I pull a gooseneck trailer with it.

My wife drove up over the pass last weekend and told me that the transmission fluid hot light came on 2 times on the way out there while pulling the gooseneck over the pass loaded w/2 horses. (It's around 12k lbs Loaded) She pulled over and let it cool down and proceeded on without any further problems.

On her way home this last Sunday, she made it about 5 miles from the house and the RPMs maxed out going up the hill to my road (2-3% grade) and she could no longer move the truck, and the transmission fluid hot light came back on. Had to tow the truck and trailer home with a logging truck.

The next day after work, I pull the dipstick and the tranny fluid is black and smells burnt. I started the truck and shifted through the gears (trailer was disconnected at this point). In drive, I would rev to about 3500 RPMs and it would barely move after a few seconds. 1st/2nd/3rd/Rev same thing. I put it in 4wd and the truck moved better, but still acted gutless.

My wife said that she heard a winding noise a few times while driving on level ground but it went away after about 30 seconds...this happened a few times.

My question is, what am I looking at hear? Does this sound like just the transmission is jacked, or could this be a culmination of the trans and transfer case? (Transfer cases switches between 2wd 4hi 4lo no problem.)

If it is a transmission, is there a kit that I could buy to rebuild this thing to where it can handle towing 12k lbs over the pass?

Thanks,

Jack