Intro and question about towing with a C35 one ton

[Blake_496]

Hey everyone! I am moderator of fsjnetwork.com where we talk about the old full sized jeeps. I built a '78 J10 Honcho a few years ago into a rock crawler and now I have built a '75 GMC C35 one ton 2wheel drive dually so I can tow the Honcho. My Dad actually had the exact same truck that he bought new in '77. Same color and everything. He had that truck on the farm and it rusted out a few years ago though.

I installed a 2005 8.1L L18 backed by a new gearstar 4L80E tranny into the C35. Swap notes include the following:

stock radiator
stock starter for a 454
stock headers for a 454
stock engine mounts
stock transmission crossmember that I moved to the rear position because the 4L80e is longer than the stock TH400

The truck is a 100% rust free Colorado truck and is in amazing condition. It rides and drives great. No issues with it at all.

My question is surrounding towing capacity. I've recently completed the truck and bought a 34' gooseneck trailer with the intentions of towing my rock crawler and maybe another rig if needed. The trailer weights 4600lbs and the J10 weights 6000lbs. I have a new B&W GN hitch (the one rated for 30K). I loaded up the jeep this weekend and took everything for a test drive. All went well, but I could definitely tell the trailer/truck was back there.

What is the max towing rating for these old C35's?