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Discussion Starter #1
Hey guys, I have a 2003 GMC Sierra 2500HD with the LB7, of course. Anyway I had a 7.3L back in the day, but I have been out of the diesel seen for awhile and just bought this truck. I have been driving it for about a week and noticed my RPMs seem to be high. At least it makes me a little nervous. I'm running right at 2000 RPMs at 60-62 MPH. Is that normal? It is all stock as far as I can tell. Am older man used to pull his camper with it so I dont think he did any mods? Any info is greatly appreciated> Thanks
 

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Sure he didn't have the rear end gears changed from the stock 3.73 to 4.10 for a little more towing power?
 

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Easy way to check rear end ratio would be to jack the truck up, put in neutral, make a reference point for your drive shaft and mark your tire either at 12 o clock or 6 o clock (for easy reference). tape a piece of twine to your drive shaft at beginning of your reference point. Have a friend make one full rotation of your tire, mark the twine at the reference point then take twine off drive shaft, measure circumference of drive shaft then measure from point to point on twine, divide by circumference and you have your ratio.

Its the redneck way but works
 

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and who said rednecks were stupid.....how many cases of beer did it take for the guy to figure that one out??
 

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yeah i am at 2000 at 70 as well the gears were changed in your truck sounds olike
 

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and who said rednecks were stupid.....how many cases of beer did it take for the guy to figure that one out??
There was a question as to which rear gear was in my first car a mustang (fox body) and this is how I figured it out.

Yeah I have always been kinda a nerd but I wanted to know what I had so I had to figure it out somehow
 

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sounds like an excuse to throw some bigger meats on it to me. go 33's man!! :thumbsup
 

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Discussion Starter #9
Thanks for input guys! I will try the measuring trick and see. Bigger tires really make that big of difference?
 

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yeah bigger tires have the effect of gearing the truck down, which with the stock 3.73's is really not the best. but since you have a different ratio bigger tires would essentially bring your revs back to stock. and it'd look good :)
 

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Discussion Starter #11
Have to lift with 33s?
 

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you'd need to level the front end. cheap way is to just turn up the stock torsion bars.

the right way (read $$$ way) is to get the Cognito leveling kit

might have to do a little trimming but a 32 or 33 would not require a lift and look dang good
 

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Discussion Starter #14
Thanks for the advice. Im new to DF and already dig it. Sweet
 

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yeah welcome to the forum man!

fill out your sig so people can help you without having to ask for specifics everytime.

be careful this place is addicting and can burn a nasty sized hole in your wallet :thumbsup
 

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Discussion Starter #16
Since we are still on RPMs. I noticed something weird today. Say I'm cruising along at 1500 RPMs and put it in neutral, my RPMs stay the same and wont go down except with the slowing speed of the truck. Normal or not???
 

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hey studlysierra I used to rev about the same as you at that speed. maybe a touch less, but now I have 37's on and rev nice and low hahah
 

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Since we are still on RPMs. I noticed something weird today. Say I'm cruising along at 1500 RPMs and put it in neutral, my RPMs stay the same and wont go down except with the slowing speed of the truck. Normal or not???
that sounds to me like the gear isn't actually disengaging, and yeah that's pretty weird. Can you rev the truck and it not have any effect on the movement of the truck?

EDIT: i just realized i have never tried this on my truck, but know on every other car i've ever driven it would drop them. didn't want to get flamed if it's some weird allison tranny thing
 

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I've thrown mine into neutral and if I remember correctly the revs dropped, but I wasn't paying attention... hmm must try this again
 

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Discussion Starter #20
ya i can rev it up but it only drops back down to where it was before; not back down to idle rpms
 
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