My truck had one of the more expensive tuners on it and it kinda hurt my mileage.
Without tuner - 11 CITY 13.5 HIGHWAY
With tuner - 11.5 CITY 12 HIGHWAY

 

Wow, that sucks either way. My truck got a high of 18 mpg on the freeway..... (pretty much empty, just me, the wife, and a couple bags of clothes for a weekend away.) And mine is a 3/4 ton.....

 

I'd bet the plenum gasket is leaking. If the cat is clogged it will definitely hurt MPG. How many miles on your truck? If you have the money, I'd replace the cat converter, the plenum gasket, timing chain set, water pump ( you'll have it off for the other stuff), thermostat, spark plugs (standard NGK), dist cap and rotor, plug wires, O2 sensors (NTK), fuel and air filters, PCV valve (Mopar), and clean or replace your IAC valve. If you've got the money, shorty headers and a dual exhaust would complement the tuner. I'll guess the tuner helps in town because with the stop and go, your plugged cat has a chance to let exhaust out when you're idling. When you're cruising on the hwy, the plugged cat is building more back pressure and killing fuel economy.

 

Thats with 4.56 gears and 35s, i was just saying that the tuner hurt the mileage. when it was stock i was getting more like 13 and 18.

 

Are you using oil too? I was getting 10mpg and going through 5 qts oil every 600 miles. No smoke or anything, running 3.55 with 35's.
Turned out the plenum gasket was blown, now I'm getting about 17mpg and not using any oil. Look down your TB and see if the pan is full of oil (even all varnished up ) Takes about a day with everything needed to change, Took me 2 days as I just took my time.

 

Happy Thanksgiving. Ate way to much of course, hope you all didn't. Thanks for all help with my truck since I got it!

I ended up ordering a $220 MagnaFlow thing.
"23285 Direct Fit Catalytic Converter(Non CARB Compliant) by MagnaFlow"
Might not be the best idea for some though. But for me it seemed like what I should do, so I freakin spent the money! Think that'll show any "noticeable" improvement in gas mileage right off the bat?

I have done the water pump since I got truck. Did it really thoroughly as well, all the hoses, everywhere, lots of flushing the engine, flush after flush(engine, heater core, rad)etc.

I wanna do plugs now after reading 2Bit's reply. And I've got to get in there some time soon to check the plenum. I think HeyYou and someone else, well, all of y'all really, has said something about that with these 2G Rams. All the things I can do for better mpg, I'll do it!

 

If anybody wants me to, I'll slap a couple before and then after it's installed pics of the exhaust. If it ever comes!

I forgot to say, right here at Thanksgiving, you all are Huge. Big, big help! Y'all are Giants in here.

Just this one post for example, HeyYou was quick with an answer, as always!, dbbd1, and again, always, Sonocativo's posts helped me out more than you think or know.

And then "2Bit" hammered out all the things to do for better mpg, plus some, all in 1 post for me, have to hunt everywhere, thanks for that-I'll def be gettin around to all of them that I haven't done yet(after the exhaust), Ramit97!-got me wanting to know which gear ratio the truck has, or whatever it's called. I know it's got "limited slip".

And fj5gtx, what can ya say. I mean, what he said makes sense! I think he cleared up the fact that It's prob not gettin as bad of mpg as I thought! My speedo shows me at 4 to 5 mph less than the actual speed I'm going. Always! Even at lower speeds, it's always at 4 to 5 mph less than what I'm actually doing! So, I gotta look into that. He might've just gave 4 mpg more by talking to me!!

Thanks to each and everyone of you all and hope y'all have a good Christmas and holidays.

 

Touching but not required. I just passing on what I know and helping how I can. Thank you.

 

Yea, I was just still in that Thanksgiving mood this morn when I woke up!
But truck really does run like new now, ever since I found this site. This is a good place for sure.

Oh yea, and I think I'm getting an 07 next week too, so tryin to stay in good for sure now!! Hehe! jk!

It's got a 5.7 though, instead of the 5.9 these have, I think 5.7 is what he said. Like 5.7 lonestar, or bigstar, something like that? Anything I should look for first? Like trans issues in those or rear end recalls, etc, before pulling trigger? He did say pwr steering wasn't acting right. I should prob switch to another topic than this mpg one. Sorry bout that!
Are the Gen3 transmissions better than the gen2's trans reputations?

Anyway, I'll def finish this one before startin anything on that one if I get it. Really do appreciate all y'alls knowledge. Its really not just some lip service like some politicians do, and my ex!.

 

Ask about the 07 in the third gen ram section. It's a whole 'nother beast.