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2003 GMC HD 6.0 - Computer settings improve mileage

opc167opc167 Posts: 14
I just bought an 03 1500 GMC HD with the 6.0l. With 152000 miles, I’m concerned with the 13.2 MPG I’m getting. I was expecting to see 16+ as long as you’re not pulling and keep my foot out of it. What I’d like to know is, I’m going to change the plugs…should I go ahead and change the coils also? I’d like to buy a computer chip but this truck to check setting but I’m not sure what to look for out in the market.

Thanks for your input.

Chris Brooks – newbee.


  • obyoneobyone Posts: 8,054
    The weight difference between a 1500 and a 1500HD is about 1000 pounds. Your truck weighs a little over 5900 pounds. Because of that 13.2 mpg is about what you're going to get. Changing the plugs may help your mileage depending on the condition of the current ones. I wouldn't change the coils unless you are having problems with the truck.

    The 1500HD is the equivalent of the 2500LD which is a 3/4 ton truck. GM had some frame issues back in 2003 where they couldn't make a crew cab off of the 1/2 ton frame dut to cab flex so used as a temporary fix, the 2500LD. Because the gross weight is over 8500 pounds your truck doesn't have an EPA rating.
  • opc167opc167 Posts: 14
    Is this the 300hp 6.0l in this truck?
  • opc167opc167 Posts: 14
    I've confirmed. It is the 300HP. Disregard my last question.

    I appreciate the input.
  • Hey Dean,this is Howard Villa.Call me let's catch up...7729461...
  • Engine codes that I was told about was to replace my "throttle body module" computer part mechanic said. I am looking for a better answer either replace the throttle body itself or the mass air flow sensor. My truck is hesitant and I have to really hit the gas to get it going. It is def. not the same power from when I first bought it. Also everytime I start the damn thing it always goes into 4 low and its tough to get out of it sometimes. I have a new alternator, battery, o2 sensors, plugs and wires. Anymore suggestions so I can stop with this money pit??
  • obyoneobyone Posts: 8,054
    The hit the gas part reminds me of those Chevies that used to have a binding throttle body due to carbon buildup on the linkage or the throttle plate. Try check to see if either has a buildup or if the throttle plate linkage is bent.
  • chuck2006chuck2006 Posts: 1
    anybody have some ideas how i can get better mpg with my 2006 gmc 4x4 truck with a 5.3 gas engine. my truck has 39000 miles and gets 12 mpg
  • How's it going everyone?

    I need some help with a problem I have had for a few months now. I have a 2003 GMC Sierra 1500hd 6.0L pick up with 86,000 miles and it will not start the first turn over. If I then proceed to try again it will start either the second or the third time. If I have driven it recently it usually starts up the first time. I replaced the fuel pressure regulator and that did not help the problem. I noticed if I turn the key from the on and off position quickly 5 or so times, it starts right away. It seems I am not getting the fuel into the motor right away, is this the fuel pump? Fuel filter?

    Any help would be appreciated.

  • I have a 2010 GMC Sierra Crew Cab 1500 pickup with a 6 speed transmission. The transmission has selections for Park, Reverse, Neutral, Drive and (M) M allows you to select from all 6 speeds. 6, 5, 4, 3, 2, & 1. You can use Drive only or move the gearshift into (M) that should first go to 6th gear at top so the transmission does not tear itself apart by dropping down into a much lower gear such as Low (1). Well my problem is when I select (M) it first shifts down into Low (1) which could destroy the tranny and who knows what else. Has anyone who owns the 2010 (or other years) GMC Sierra 1500 pickup had this happen?

    Help me please. CAH
    Read more: /index.html#ixzz1401Tkoaw
  • I just bought a 2003 from a dealer in Sept. had the same issue going right out of the dealership... they made it right... twice... fuel filter and fuel pump in the tank was also replaced... it worked until I ran out of gas at 1am in Iowa on I 80.... then they took the tank off again and fixed the wiring of the fuel pump for me..... so far no charge and this was done in November when I came back with an extra 4,000 miles on it.... they are still working with me with fuel gauge.... still got troubles.... So what I'm saying is the computer is not seeing fuel coming so the fuel pump must be clogged>>>>>> that is what I'm saying...
  • I had same issue with my 01 silverado I replaced the fuel pump. right now I have same issue with my 01 1500 hd about to change fuel pump. hope thi s helps.
  • I've been driving an '03 GMC Sierra 1500HD, 6.0L since 2006, bought it used w/ 45K mi. and have had NO problems w/ it other than normal maintenance. The speedometer is gone but the odometer's still rolling, just turned 129K. The message center is indicating "RFA 1 low battery". I've searched only on-line and can't find what this means. The battery was replaced a month ago. Everything is running fine...for now. I had an issue w/ the oil pressure gauge this weekend. The needle was all the way to the right. It's working fine now, all fluids are fine too. Just curious if I'm headed for any surprises. Just want peace of mind, this is my one and only vehicle other than my wife's street legal golf cart! Is there anyone that can coach me on whether or not I have any potential issues?
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