The past two weeks I've noticed my mpg drop from 15 1/2 to 12 1/2 in the city. I drive the same distance everyday to and from work, and mostly is rush hour traffic. I don't punch the trottle too often but when I do I leaves behind a cloud of black/gray smoke out of the tail pipe. No codes are being displayed on my dash, but my service tech at the gmc dealership I bought it told me to bring it in for a look, says the mpg shouldn't drop that much. What could be the problem??:o: I'll bring it in on Monday the 21st to find out..

I've heard that the news ones do this.. mine did it as well. It drops at first then creeps back up. Mine dropped to 12 in the city and is now at 15.

How many miles on the air and fuel filters? That will be the first thing to check if no codes have been set.

4900 miles totalHow many miles on the air and fuel filters? That will be the first thing to check if no codes have been set.

My '05 GMC did the same thing. My first 2-3 tanks I got 16 mpg. It steadily dropped to 13.5-14.5 after about 4000 miles. I am at about 5300 miles now and mpg are at about 16-16.5 again. I don't know if the Predator has anything to do with the recent increase or if it is just the truck. These numbers are with my wife driving the truck with an average trip of 10 miles. I haven't had been on a road trip yet so I don't reaaly know what it will get with all hiway miles. I am planning to go aon a long trip this weekend pulling my 14' gooseneck horse trailer. It will be interesting to see my mpg.

Well my first tank on an LLY was 13.3. Second tank to 14.7. Moderated itself out a little higher, but nothing like what some people are talking about (i.e., I'm getting about 15.5-16 overall and consider myself to have a very light foot). But then again, I'm running 295's in a 50-50 mix of city/highway, so I don't have too much to complain about. I wouldn't have bought a truck if I were that worried about mileage, but it does tick me off that others appear to be getting upwards of 20 mpg.

I am seeing about 15mpg on the hiway (75-80mph) and around 11 in town with about 6500 miles on the truck.

Last week I received the re-flash, but I haven't checked the MPG yet. I am trying to be patient and track my modifications to see which, if any, help mileage.

Mods:
1. Reflash
2. Standadyne additive;
3. Predator 65 tune.

The Predator is last because I probably won't be able to keep my foot out it long enough to check mileage :p: . The additive will probably show some benefit over time.