My first truck had a 105hp 275 torque 292 I6, that was an 81 2500 with 8600 GVWR. Slower than snot! My next rig was a TBI 454 with 235Hp and 385 torque. A bit faster, but could not pull a hill for its life, ie a short steep hill! Anything over 15% it stalled out at around 12K total wt. Meanwhile that lowly little 292 went up the hill, fetched a pail of water, went down, and literally pulled the 454 up the hill! HP is part of the equation, as is actual torque, along with overall gearing!
Some of us do not need a BIG motor in our 25 or 35 series trucks, Only enough to mover the truck if all you do is haul stuff, or maybe a smaller boat or rv with a load of people. I would take one of the smaller 5L V8's or the 4.3 in my current 2000 C2500 with the current 4.10 gears, the 6 sp auto. Probably have some 50+ more HP, and about the same torque as the vortec 350 in it, getting better than 12MPG too! I do admit, it needs a tuneup, did get upwards of 17 at one time.......still not as good as 20+ that most 4.3's get. WHen they came out, they had less than 160HP!
Oh, the gasser did not do well in the mtns.......my 7.3V8diesel does not do well in the mtns either........Nor do too many non turbo/supercharged/forced induction motors no matter the fuel type! Put a supercharger on a gas rid, now compare to an equal HP/torque diesel, both should do similar speeds etc. Otherwise, at 10K, the non forced induction motor is down upwards of 20-30% of its HP!
So for those with a too small of something, trying to make up for a larger HP motor etc, stuff it! small motors will pull things just fine. Only takes 10HP to mover 100K lbs at 1MPH!
Marty