Tough to diagnose at this point...does the truck feel peppy? Is it shifting normally and keeping the RPM's low in normal driving? Does it coast freely? When my truck is in overdrive, even the slightest downhill grade will let me maintain speed or accelerate.

I'll just brainstorm anything that might be hurting mileage...assuming you have no CEL's

Bad Intake sensors
Clogged cats
Bad O2 sensors
Low tire PSI
Filthy air filter
Engine oil sludge
Running with O/D off
Slipping transmission
Bad spark plugs
Stuck brakes (Who knows if the mechanic checked them or not)
Piston blowby - bad rings
Dead cylinder(s) (not likely without a CEL)

Driving style. Some people think they are taking it easy and aren't, just saying. My Ram 2500 work truck, 5.9 Gasser with the 5 speed, went from 10.5 MPG to 14.5 MPG when I backed off the skinny pedal. Granted I can choose my gears, but that's a big difference.

 

My dad is out driving it to see if he can get more mpg.

I don't know where to take the truck. No one is finding any problems....



Dad just drove 100 miles and filled ip. He got. 19.3 mpg. 95% highway driving.

HUD says 18.3 mpg.

 

We seem to have one every couple of months. I tink you need to be careful comparing youself because some of the guys on here might have 2WD with a manual tranny and thier MPG is gonna be WAY better than me with my 4WD QC V8 auto.
I had the V6 in 05 (new one I turned in at lease end) QC, 4WD+auto tranny and I used ot get just under 14MPG around town. I now drive a 07 QC 4WD V8+auto tranny and get similar milage (actually I get just under 10MPG but that is running e85 fuel so add about 30% to get milage w/ u87 pump gas.)
Lastly, some areas don't have hardly any ethanol in the gas, so you will get slightly better MPG there too.
I think the thing that really chews my MPG is all those flippin' speed bumps and stop lights as well as a REALLY short commute (less than 5 miles.)
When I drove the same truck down to FL and back last year I posted the numbers and they were MUCH better in straight highway runs.

 

Mine's a 4wd club cab, v8 with a six speed manual...

At 62 or so I pull about 22mpg on the highway, the overhead usually reads 21.7 or so, hand calc's put me at 22.1 or more...

 

I'm still stumped. I drive generously in the city (that's where I drive 95% of the time). I don't know what I could be doing wrong. Accelerations aren't rough. I never slam on the brakes. Im not a rough driver.

 

I have an 06 Quad Cab 4.7 6speed 2wd. I typically get 15-16 around town and if I do a lot of highway driving it will be 18-19mpg.

If the tires are oversized that will make a big difference. I have a 90 Dakota Sport that came stock with 235/75/15s but had 31s on it when I got it. I put the stock tire size back on and the mpg went from 14.5-14.7 most of the time to mid 16s on average.

I think you said the truck had 55k, it's probably time for a tune up (plugs, wires, air filter, fuel filter, pcv valve).

 

Great info right there boys

 

So your dad went out and got 19+ highway? Right on the money!

95% city driving, depending on the city, might only be good for 11 MPG. Short trips and idling are the worst. If pops only managed 14 or 15 on the highway, you might have a problem. But it doesn't appear your truck is working any harder than ours during high speed cruising.

Try a PCM reset and maybe the truck can re-learn with your city driving style.

 

a trip to six flags including some city driving and traffic averaged just over 16mpg. Thats including the great safari drive through thing which took over an hour to drive 14 miles.

 

how do you do a PCM reset? sorry for the double post