Back when I owned a 96 Chevy K3500 with the Vortec 7.4 automatic with 4.10's, I would occasionally help my BIL tow his hay trailer which weighed 15k +. Towing this weight, the Chevy would not pull overdrive on the flats. Compared to his 97 Ford F350 PSD 5 speed manual with 3.55 gears, which would easily pull overdrive on the same route, it was obvious the low end power of the diesel was a better puller. Now if I wanted to let the 7.4 rev a bit, it would outpull the PSD on the hills (4000 rpms), but the fuel mileage was really the biggest difference. The 7.4 would get 6 to 7 mpg, whereas the PSD was getting 11 to 12 mpg.
I would also pull an approximate 7k travel trailer with the Chevy across Nevada on I-80. The Chevy had to run hard to pull 3rd (direct) with this trailer on the hills, sometimes dropping into 2nd to maintain speed. Again fuel mileage was around 8 to 9 mpg on this drive. I later bought a 2002 Dodge CTD 6 speed manual with 3.55 gears. On this same trip with the travel trailer, the Cummins would pull some of the hills in 6th, with a drop into 5th(direct)and run right up the hills with out further down shifts. Fuel mileage was 12 to 13 with this combo.
Now I know that comparing the 7.4 isn't the same as the 8.1, but it doesn't have that much more power than the 7.4, and where it does have more power is higher in the rpm band. Empty with the 7.4 I'd get at best 13mpg, where the Cummins would get 18 to 20.
I'm not knocking the gas engines. I really liked the 7.4, especially when it was empty as it would really run. As with any gas engine, you just need to let them rev and they will pull. But get up in elevation with grades to pull, and have a head wind, the Diesel is hard to beat.
Rich
