Just think how much gas you could buy for the 300 with the money it will cost to do a diesel swap. Doing some quick calculations and assuming 13 mpg with the 300, 25 mpg (probably closer to 20 though) with the diesel and a VERY conservative cost of $3,000 for the swap, it would take 30,000 miles to break even. Lower mpg with the diesel and higher cost for swap and that figure grows. About 6 years ago I owned a 2wd 2000 Ford E250 EB with a 5.4L. I would average 13-15 and the best I ever got was 16 mpg. At the same time, I worked for a company and I drove their 1999 4x4 Ford E350 EB with 33" tires. It would average about 16 and the best it got was about 18 mpg. :smilies27