I bought a new '02 ram 1500 4.7L. It made it to 145K miles before the cats warped the heads. Got 14mpg, about 7mpg when pulling the TT.
Then I bought a new 2005 ram 3500 5.9 Cummins and it now has 289k miles and always much better fuel mileage. It's barely broke in and will be the last truck I'll ever need.
Your results may vary.