99 PDS 4x4 i get betwwen 12-20mpg depending on trailer/no trailer, my foot, the temp outside (can make a big dif!), city/highway, ect.. i have a chip (110hp) 4 1/2 inch exaust. (the air temp outside can make a big dif., if the engine isnt at temp. then its not running effeciently... so it will burn more fuel, this is why you see semi's with the covers over their grills.) with out a cover, in the winter i get 9-11 mpg, with a cover i get 13 (with 3000+lbs of salt + spreader and plow, ect..) all winter. quick trips (start drive 2 miles shut off) use alot of fuel. its most expensive to START your truck and to get to your speed your going to stay at, once you reach your speed a diesel engine uses hardly any fuel to stay at that speed, the things that would change this would be.. a change in grade (an incline) head wind (wind comeing at you) ect.. (a 7.3L PSD uses 1/8gal per hour to idle, THIS IS STOCK) I have worked for ford and gmc and they both make a good truck. im not a big fan of dodge but they make a good truck too. But they all have their flaws and +'s. one thing i dont like about the duramax is alum. heads, IMO this wasnt a smart move. the new fords (6.0L) have had ongoing prob. with the computers programing, i know a few poeople who have had to get reprogramed 5+ times and they still run like sh*t. and well i already said i dont like dodge, so i will leave that one alone. Buy what you can afford. Buy based on your experance.. ie if you hate a particular car company .... Dont buy from them. buy from a dealer who you like.. and who has Great service...Unless you plan on doing your own work. (i wouldnt sugest this unless you know diesels, you could make it cost alot more $!) hope this helps someone out.