Background ...
Had a GMC 8.1/Allison and now an 07 PSD
Trailer is a 28' tag weighing about 10,000lbs
Reese twin cam WD/Sway system

First impressions ...
Loaded, the Jimmy is a great truck, but it would never spin the tires leaving a stop light nor bark the tires when hitting 2nd gear.

GMC?

Second impression to come ...

 

Your GMC never had the leg room either you will find your new truck pretty amazing to tow with.

 

I previously had a '96 F250 with the 460 V8, Auto, 4x4, 4.10 rear and was really quite happy with the way it towed, a great low end engine. My trailer is slighly less than yours (about 7,000 lb) but close. It would certainly slow to 40-45 on long or steep hills but once it downshifted, it would pull about anything. Of course I got 10 MPG empty and 9 towing after putting on headers (got 7 towing before headers). Then I got the PSD, my first diesel about a year ago. '06 6.0 Auto, 2x4, 3.73 rear and boy was I surprised. Solo, the old 460 actually felt like it had more power, really a head snapper. The 6.0 will definately set you back but probably due to turbo is not as quick as the 460 was. That is where the comparison stops though. Pulling anything the PSD does not even breath hard. Pulled the same trailer over Cajon Pass a while back. The 460 would have been at 45 for about 10 miles, no problem pulling just could not pull it in the high gear. With the PSD, I was doing 65 (if your a cop, I was really only doing 55..officer..) and could accelerate from there at any time. I had to slow several times due to traffic then could quickly gain back any speed I wanted. It was really a good feeling to know that any power I wanted was there, just press the pedel.. For pulling, will never go back to gas. I also get better mileage pulling with the PSD than I did solo with the 460. I am currently running 15-17 solo and 13-14 towing.

 

I still have my White Rhino (88 GMC CC 454) 4:10 rears and comfy when loaded. You put the throttle to the floor, set the cruise, and watch your engine temp gauge go to max on steep grades. You can pass anything on the road except a gas station.....

The diesel is way better to tow with especially on long trips.