I have the 5.3. Gas mileag decent, better than I expected from a truck. City about 11-13, highway about 16-17, towing 10.5 mpg. The 6.0 uses more gas than you would expect the .7 liter difference to make. But this is from talking to those who have them. Great engine though. I know the tow rating is similar between the two, but you will enjoy a bit more power out of the 6.0.
Having said all that, here is another fact to add to the equation...you can only get the 5.3 in the half ton, (1500) and you can only get the 6.0 in the 3/4 ton (2500/2500HD). You can't get the 6.0 in the 1500 and you can't get the 5.3 in the 2500! So, deciding what engine to get is ultimately deciding which truck to get!
I will speak for the 5.3 though, which is the largest motor you can get in the 1500...it is a very strong engine, smooth, powerful, and will easily to the maximum trailer weight if asked to do so, which I would never again tow near my max. Learned that a while ago!
2009 Silverado 2500HD 4X4 C/C/6.0/3.73/Pullrite Super 5th.
2004 Puma 249RBS fifth-wheel bunkhouse.USAF/GULF WAR VET.
I get about 14 mpg highway with my 2001 6.0 2500HD. Towing is about 7 mpg average, keep in mind there are a lot of hills here in Vermont. On the way to Atlantic City this fall I got as much as 8 1/2 mpg and as little as 6 mpg. Power is ok, I am pulling well over 8000lb as my 5th weights 7600 dry. I would not pull a heavier trailer with this motor, I would go with the diesel. It is plenty of truck for that weight (handles good, stable, and good braking), I would just want more power in the hills. It will slow you down to 45mph on the steep grades here in Vermont and is working the motor pretty good, but on flat going 65-70 mph is no problem.
I have a 1/2 ton Yukon XL with the 5.3 Vortec engine. We get 14-16 around town and 20-23 on the highway. Have the 3.73 rear end, 2 wheel drive w/posi-traction and traction control. Use synthetic oil and trans fluid. Added K&N air filter, Poweraide throttle body spacer, and Grantelli mass air flow sensor. You can definitely hear it sucking in more air. I think with a catback exhaust and a reprogramer or chip, it would be as strong or stronger than the 6.0 and still deliver excellent fuel economy. Have 28,000 + miles on mine and absolutely no problems at all. Bagman.
I have a 6L and I average 12-14 MPG commuting. This is combined city and highway. Highway I have had 16.5 MPG. Towing I average 9-10 depending on terrain. I haven't done any mountain driving, but through the Texas hill country I got 9.
*This Message was edited on 12-Feb-02 03:36 PM by Joe Weber*