I've dragged my 8600-lb trailer into the Rockies several times with my 3/4-ton Suburban.  6.0L gas engine, 3.73 gears, full complement of factory coolers.   It's rated for 9300 lbs max towing.  I'm right at my maximum rating of 16,000 lbs GCW.




Eisenhower Tunnel - 11,100 ft, 7% grades, I-70 with 3 lanes
Was I winning races? No
Was I impeding traffic? No
Was I faster than the big rigs? Yes
It seemed to hit its sweet spot at 40 mph, in 2nd gear, at 4000 RPM. Still faster than the big rigs. Coming down, it was simple to control my speed with engine braking, only occasionally having to hit the brakes.

Powder River Pass - 9,666 ft, single lane road with switchbacks
Again, was I impeding traffic? No
Coming down was more interesting.  Was winding the engine as high as 6,000 RPM, while having to apply brakes at sharp switchbacks.  

The A/C stopped working half-way through the descent, and I'd thought I'd killed the compressor by spinning it too fast.  Truck has a separate A/C belt, it's not run off the main serpentine. When we finally got down, I popped the hood and saw the A/C belt hanging off the crank pulley.  Went to an auto parts store, bought a new belt for $11 and paid a local mechanic $50 to put it on (it's at the bottom and a PITA.  Total down time: 2 hours.

Plan far ahead, and apply the brakes in bursts, don't just ride them all the way down a grade.  Learn the combinations of gear/engine speed that produce maximum engine braking. Then use your brakes to get to those points.

Make sure you have a way to monitor the trans temp.   That would be my biggest concern.

Make sure you have fresh fluids with plenty of life left - oil, trans and engine coolant.

Know your vehicle's limits, what temperatures it can handle.   This was my worst, still within "reasonable" limits.