Mr.Beebo wrote:
The diesel posts are for another thread.
To answer the OP, yes, there are gas motors in the 3/4 & 1 ton market that will more than ably pull 13k thru elevation. 6 speed transmissions make a huge difference as well as 4.10 gearing. To 2nd the post above from Fishbreath, the gas motors wind out when they need to; that is where they make their power. Doesn't bother me a bit and it shouldn't, as that is what they are made to do. I can pull 9k at 60mph running about 1900 rpm or I can run at 3k in tow/haul and it sounds sweet and smooth as powdered sugar.
My towing story is not of heavy towing, but the 2 trailers I tow are..... a very tall 3800# Hybrid, and a normal height 24'TT (basically a Rockwood Roo)6000# loaded. The 3800# Hybrid is a noticeably harder tow on the flats. Ive crossed the Rockies, via Colorado 4 times with an F150 with the 3.7.
On the flats, 65ish (sometimes 70) the tiny, inadequate, joke of a motor, not suited to a truck.......Pulls both in 5th, at 2200rpm steady, even into a light wind. Into stronger gusts, 4th gear, 2800ish rpm. (Getting the same 10mpg as my dads 4.6 V8, slightly better than my old Tacoma at 9mpg)
Climbing the Ike pass, lots of 3rd gear, 4500rpm (with a nice growl on the 2013, 2011 was just a bit too noisy). and on a number of occasions, 2 gear, because I just set the cruise and let it shift. Other than the relatively brief times at higher altitude where horsepower is down, I enjoy the fantastic economy (purchase, cost of ownership, and fuel mileage) of owning the base engine. I don't have all the hangups and ego issues associated with not having the bigger engine. Fact is, 300hp was a class leader in half tons 10 years ago. I can unhook, drive to the lake, getting 21-22mpg at 70 mph, and go 0-60 in under 8 seconds.
Hope that helps with the OP's original question.