I towed many trailers with my n/a 1992 and it really didn't like hills or altitude. When I towed a car hauler it was literally third gear 3/4 throttle or better on some steep legs of most passes. It really didn't really hurt anything. Well maybe my ego....nope. It was unloaded most of the time so the occasional slow tow was fine with me.
I can tell you that a turbo will make towing a completely different game. Although I don't really love my Powderchoke, when towing at altitude it's really hard to compare the two as the performance is really night and day versus my old IDI.
All the other stuff will help marginally: a turbo will change your truck majorly at altitude.
Tough decision ahead of you, but you'll be fine whether you keep your rig set up as "Smokey"
or turn her into "Little Whistle"