old motorhead

iTrader: (10)

I usually get 325 to 350 as long as i'm being fairly steady with my right foot. It did a little better when I had the 4L60 tranny. You might look into a custom tune from one of the sponsors. Nelson Performance has done quite a bit of work for me and he's always been very good. When my 5.3L had just headers, intake, and a Nelson tune, it would get 20 mpg on the highway. The 6.0L won't do that no matter how sane I drive.

sonoma43

iTrader: (1)

IMO it is the hyperpac causing some of your problem it seems to me that any handheld is junk for tuning, they are useful for changing shift points, top speed limiter, etc... But when it comes to fueling and timing they arent worth a broke dick. I've seen dyno runs where they lose power (over stock) and the timing tables on them look like roller coasters.

clemsondave

I agree. Find someone with HP Tuners and have them take a look. They can also tell if the O2 sensors are not responding correctly. Maybe they got trashed somehow.

Check plugs. Make sure they all look ok.

Just before pulling my 6.0L apart due to issues and 200k miles, I was getting around 330 miles out of my 27 gal tank.

Fireman31

clean your MAF and TB also........

budhayes3

iTrader: (19)

Well your wheel and tire combo is basically what comes stock on the Silvy SS's, so that shouldn't be a big problem. Yea, a lighter wheel and tire combo will help, but I don't think that is the biggest issue. I'd start from scratch and make sure that your tune-up items are up to date (with only 42k the plugs and wires should be fine, but it couldn't hurt to check the gaps), make sure the MAF and throttle body are clean, check the air and fuel filters, then ditch the Hyperpac and get a tune from one of our sponsors (Blackbear, Nelson, Wheatley). I'll bet that if you got the tuning spot on you'd see a noticeable improvement.

wht01ws6ta

iTrader: (42)

Does your hyperpac come complete with a wideband O2 sensor? 13.4 is fat for cruising around.

You can only put 23 gallons into your 26 gallon tank when it shows E because that's GM's way to keep people from running out of gas, the gauges are calibrated that way.

Fill up, reset your trip odometer, run to nearly empty then fill up again and divide the miles traveled by how many gallons you just put in. Don't just go off of the gauge.

And the GPS suggestion is a good one to make sure your odometer is reading correctly

You scanned to make sure there are no DTC codes, right?

viciousknid

iTrader: (8)

I'm wondering this as well.
Without it actually plugged into the exhaust it doesn't know what the AFR is. It's just telling you what it thinks it should be.

Mine runs around 15.2ish at cruise and 12.8 at WOT

BuyAmericanIron

I strongly agree with the guys telling you to get rid of the hand held "tuner" and get a real tune. Throttle body, MAF, plugs and wires are good ideas, but the plugs should turn on a light if there is a misfire. One thing not yet mentioned is the fact that "winter gas" is a different chemistry. It is made to be more volitile for easier starting in extreme cold weather. In the process, it costs less to produce and therefore the price usually goes down a couple cents about mid to late October. This "winter blend" has lower BTU's so your fuel economy will drop a couple of tenths. Next thing not mentioned is how long you let your truck idle to warm it up in the morning or before driving? Also, short trips use a richer fuel mixture causing a drop in fuel economy. One last thought is to try filling up at a different station. Try some "name brand" gas. You might be surprised. My truck is an 08 Sierra Denali with a 6.2L and it is mostly driven short trips, less than ten to fifteen miles most of the time and it is getting between 12.5 and 14 MPG since the cold weather set in. Just a few ideas to check out. Good luck with your project!

budhayes3

iTrader: (19)

Good point, I was thinking of that then forgot to mention it lol. We've seen around a 2 mpg drop from the "winter blend" that's offered around here in Jersey.

BLK WDO

iTrader: (5)

Ryan_prettyman....

what gears u running?

im running a rcsb 06 gmc 5.3 flex fuel too. on 20's (heavy SOB's) with factory plugs, wires. Ram air intake, hptune........ with 3.23 gears and i get 18-20mpg hwy and 17-19 city. ( thats 414 a tank i think)