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Discussion Starter · #1 ·
Hey guys just sold my 2003 LB7 and got a 2007.5 LMM. I love it so far but looking for moderate upgrades and I wanna keep it as stock as possible. All suggestions are welcome, thanks guys!!
 

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Aftermarket tuning will wake the engine up. The previous owner of my last LMM had a Hypertech Max Energy which was great, had 3 settings but couldn't change tunes on the fly. That was my biggest complaint. The Hypertech tunes were "safe" and not extreme tunes. Big difference though and I loved it.
 

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2003 GMC 2500HD 4x4 Banks Super Scoop, Banks Rear Dif Cover, Mechman 320A alternator, S&B fuel tank
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Lift pump is a good place to start. FASS, Airdog or Kennedy are all good choices.
Swap the fluid out in your transmission for Transynd or equivalent.
 

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Tune it. Fluid swap it all so you know on a used vehicle is always a good idea. My tranny flush caught me by suprise oooph....alotta oil. But none the petroleum products are cheap now, it is what it is. How many miles?
 

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Ditto what these guys said:

Change ALL fluids. I'd use transynd in the Ally and Amsoil in the gears/tcase and whatever you fancy for Engine oil and lube. My local Allison service place said they only replace the internal filter upon overhaul. Others have differing opinions. If you drop the pan, change it for sure... but your truck, your call on dropping pan just to do that.
Side note: local United Engine place is where i get my Allison stuff. They said they can plug in and do a diagnostics on the tranny and find out life left, etc. Mine said they'd do it for free. Might not hurt to look into this since its a new-to-you pickup.

Check your tranny lines. If they are the rubber-crimped ones from stock they may be leaking or likely will start. Known issue with LMM but easy to fix. If you run flex lines its an easier install. I did aftermarket hard lines with short SSbraided lines and it was time consuming.

Check your fuel lines, the 1/2" ones. the 3/8" ones are the return and unless leaking, have not caused any issues i've read about. Couple of spots to check:
  • crossover at fuel cooler
  • crossover at tranny
  • line on drivers side near firewall
  • post-filter head
All are rubber and the stock ones (cheaped braided ones) will get soft and suck shut under high loads after a while. Hose aint cheap per foot but get Biodiesel rated hose and you'll never see this problem. A lift pump (LP) will somewhat fix this as it provides positive pressure (vs a vacuum when in stock setup) but replacing the lines is easy.
I would say replacing these fuel lines is the second thing you do after changing all the fluids. All you need is a dremel and a flat head to take off the old lines. New hose and some GOOD, SOLID, SS hose clamps (dont be like my neighbor and buy them HF crap hose clamps). Home Depot/Lowes sell some individually that have served me well.
 

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Everybody above pretty much hit it on the head. Good luck finding quality tunes in the current EPA climate. How many miles are on it?

Currently at 268k on my LMM no real issues aside from some electrical gremlins that caused a headache.
 

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Discussion Starter · #7 ·
It has 218k on it and on the car fax the transmission fluid was changed about 3k ago. But for piece of mind I might just start going through and replace all the fluids
 

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2007.5 Chevy Silverado 2500 HD
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Cool I just got one also. Same year 140k on it! I changed all the fluids and external filters! Had a code for glow plugs so changed those. Just finished AD 100 install today!
 

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Sighhh.... i think i need to ante up and do the lift pump. been lookin at the AD 100gph as well. Plan keep this truck forever. I'll never be able to trade my home for a new one!
 

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Sighhh.... i think i need to ante up and do the lift pump. been lookin at the AD 100gph as well. Plan keep this truck forever. I'll never be able to trade my home for a new one!
If you plan on keeping the truck for a long time one thing to consider as a future mod is replacing the fuel tank. The crew cab short beds only came with a 26 gallon tank, stupid small if you are towing a trailer. Did a S&B 62 gallon install on mine 08 and have been kicking myself for not doing this sooner. I can now pick and choose when I want to fuel up. Easily a 1000+ mile range now. They are not cheap but definitely a worthwhile investment. Works very well with a FASS or AD lift pump setup. Dean
 

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I second the bigger tank. I put in the S&B as well. Havent towed yet but... i used to fill up around 20gal. Doing the tank utilization (20/26 gal) with the S&B (47/62) @18mpg I can go 850miles. @12mpg (towing) I can go 572 miles.
 
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