I pulled a smaller trailer with our 1991 Suburban and never felt any great lack of power. It has the 350 TBI with 700R4. Never use OD when towing, and I did find that it works better to manually shift down to "2" when you start losing speed on a hill. Otherwise it slows down to about 30 mph in Drive and then shifts to 2 and runs up to about 50 and shifts back into Drive and starts slowing down again. Put it in 2 and it lopes up the hill at about 45-50 without any strain.
Unless you just absolutely
have to top every hill at 70 mph, mountain roads are usually curvy enough to make that too fast anyway. That's what the slow lane is for
One time we rescued our friends in their mini-van up in the mountains. We rented a u-haul dolly and towed their van full of camping gear along with the five of them in the Suburban. Of course, my wife and kids had to go along so we were plum full with four adults and five kids along with four dogs, and their loaded van on the dolly behind. There's a pretty good little hill down by Columbus where I-90 leaves the river for a while and we cruised right over at 70 mph with the AC on