Hey i just joined and own an 02 dodge cummins 5 speed and a 91 dodge 3/4 ton 3 speed automatic. I was just wandering why it is that even with the 91 3 speed not having an overdrive it still gets better mileage than my 02 running at the 70-75 mph range. I get about as many miles out a tank of diesel in the 91 as the 02 and the 91's fuel tank is 10 gallons smaller!! Granted my 91 cant run like my 02 but just wandering why theres such a big difference in mileage

Also if any one wants to see a sweet video of a 95 cummins smokin like a freight train or the fastest only diesel 3rd gen cummins go to :

http://www.relentlessdiesel.com/forum/viewforum.php?f=7&sid=47e0e50ad1510d1cc2038fbc3e0d83eb

From what I hear of the older 12 valve engines is the gas mileage is quite a bit better. My 04.5 can manage 18.5 running about 65-70 on the interstate not towing. Might crack 20 mpg if only driving 55 but that's a little difficult for me and not verified. I understand some of the older trucks are getting in the low-mid twenties. More horsepower=less mileage.