I’m not at all familiar with the Enclave so don’t know if we’re talking a six or an eight cylinder, or what the gear ratio is. However, I was born in Colorado and raised in Colorado and Wyoming and now live in Idaho so I know a bit about mountain challenges.
I had never towed anything over the passes until I got my first Airstream, a 1969 31ft. I pulled it over numerous passes in Colorado, Wyoming, and Idaho and have pulled my 34foot Limited over many as well. My first TV was a ’79 GMC, 350 automatic (carbureted). I pulled Monarch, Blue Mesa, and Rabbit Ears with it (hauling a 750 Honda cycle in the box). I replaced the GMC with a wimpy 6.2 Chevy diesel (no turbo) and pulled Monarch several times, as well as pulling several Montana and Idaho passes (also with the Honda in the bed). After I got my Limited I pulled Monarch as well as whatever is around Jackson, Wyoming with a 5.7 Chevy 1500
((gross overload—I don’t recommend this). It wasn’t much fun and I held my breath a few times wondering if I’d make it, but with patience and caution, each of the trucks did what I asked of them. I’m a fanatic about auxiliary transmission oil coolers and that may be what saved my bacon a few times.
There is a formula for determining your horsepower loss per 1000 ft. rise in elevation. I think it is something like 3% loss per 1000 ft. This would mean your Enclave has 1/3 less horsepower at the top of Monarch. Of course if you are equipped with a supercharger or a turbo charger there won’t be so much loss.
If you decide to try it remember that what goes up must come down. Don’t ride your brakes or you’ll lose them fast. If you’ll slow down way slow at the top (like 20mph) and drop it into low range the tranny will stay in second gear and give you some degree of engine braking. When you need your brakes, get on them hard and quick, slow down to a bit under the speed you are comfortable with, and get off the pedal (if you don’t need too much brake, use the trailer brakes only, fast and quick). The previously mentioned braking problems often are caused when a driver over-uses or rides the pedal. When this occurs three things can happen; 1) you’ll glaze the surface of the pads or linings, 2) you can badly warp the rotors or the drums, 3) you can boil the brake fluid and boiling fluid won’t stop you.
I join the folks who have stressed that you can’t have too much power for your TV. Of course if you only need it on rare occasions I can understand pushing things, I’ve done it a lot. After I got my present TV there have been no more white-knuckle pulls. There have been a few white knuckles on the downhill side, since I don’t tow enough passes any more to feel like I can justify the expense of an exhaust brake.