I have an '05 LLY. Fuel filter changes are a must. I run 1/4 qt of DieselKleen and 1/4 qt of TWC-3 2 cycle oil with every fill up. Provides a noticeable difference in injector noise.

LB7's have injector issues, plus because they are under the valve covers, it is a BIG labor bill to replace them.
LLY's can have Head gasket problems when running tuning or if you let it get too hot.
LBZ's crack pistons when running big tunes.

All need tie rod sleeves, the tie rods are thinner than the ones on my Maxima. 4x4 launches will break/bend these. These are cheap and easy to do (just did mine today actually).

Stock Allisons cant really hold much more than 400 wheel HP, the newer models can hold a little more, but still living on borrowed time. A full build if you get it done will run about $3500-4000 but will never break or slip. 500-550 wheel hp is a simple matter. EFI live and a lift pump will get you there.

Have fun.

here u go,, 252k miles, dpf delete kit turbo back, edge tuner, and once u reach the around 225k miles, little gremils come out and attach themselves to ur wallet. I have a fuel, low pressure issue that no one can find the cure for. the info u get from the forums on duramax are up and down for info. be prepared to find the problem yourself thru research and $$$$$$$. good luck

Since OP sig is not filled out to know where from........
I second, if in Emissions controlled area, 06-07.5 classic would be best, but you are now looking at trucks 5-7yrs old.
If emmisions are not a worry, the 07.5-10 have nicer interiors and more stock power. DPF delete and an EFI live tune gets you in a better place than a Classic. Keep it under +70hp tune to be safe on the transmission. This will void any remaining warranty but you dont have any warranty with the older trucks anyway. You can have the dealer scan the ECM to check if there has been tuning done which may indicate prior owner ran bigger power and may have done some damage. (maybe not enough to see, but "limping" it once or twice will show up at some point)
Also second keeping stock tires to minimize front end issues (and better milage)

I have a 07.5 NBS. I am sure the DPF is somewhat restrictive but not too bad as long as you run enough miles the regen occurs on the highway. A much greater amount of fuel is consumed to complete an in-town, multi trip regen. Really pisses me off. Regen also has an uncanny habit of starting when under a 1/4 tank

DPF may be falling off in 6 months, have not decided yet????

Using quality fuel, an additive like Staydyne and a lift pump/pre filter like FASS or AirDog will provide cleaner fuel which creates less particulate thus less regen. also takes work off the exensive to replace CP3 (fuel pump).

Dieselplace.com will help you out with almost anything you need.

I just picked up an 04 LB7 in October. Loaded with every option, 3500 crew cab dually with 145,000 miles for under $10,000. Just did the injector replacement on all 8 cylinders. Parts and labor, $2800. I now have an Air Dog 2 lift pump fuel filter and water separator and a nictane filter (Caterpillar truck filter with adapter) in place of the stock fuel filter. One of the main reasons the injectors fail was because of the junk fuel filter setup that GM had in place. A fuel filter and water separator combo is not a good combo. The water expands the filter from 2 micron filtering and allows 5 micron particles to pass through. The trick is to treat your fuel, do not buy junk fuel, make sure it is filtered properly for water and fuel filtering, and get the filters changed every oil change.

Have you tried shimming the fuel rail? PPE makes a kit I believe. Sometimes tuned trucks will throw the low fuel rail pressure code, shimming the fuel rail usually fixes this. Or is your problem something more serious?

Just traded (5 months ago) a 2003 2500 crew 2WD SLE 170K+ miles, 7500 hours on the motor. Bought new, nothing first 100K miles, 106K did a water pump, 130K one front wheel bearing (did both and 1st brake job at that time), 145K GM did the injectors for free.....Truck was bone stock except for a K&N filter. I got 9K for the truck on the trade, they listed it for 10,999 and it was sold in one weekend (no haggle dealer). Not sure if they put tires on it, they were thin when I traded it.

Great truck, no issues but the shocking thing was the cost to run it! I spent more in diesel fuel than I spent on the truck! Truck got 12-14 mpg (hand calculated, 280 miles on 20 gallons is 14 mpg, not the computer guesstimate). So if that truck got 13 mpg over its lifetime I bought over 13,000 gallons of diesel. Even at $3 a gallon that is $39,000 in fuel for a truck I bought new for 32K (msrp was 43, but they had a 3K rebate on the diesel trucks in 03 and it was a leftover).

The 39K in fuel was a shocker, truck was a daily driver overkill for 90% of the time.

I had an 05 2500, great truck but did have injector problems. I now have an 08 3500 dually...good so far. The 05 was better on fuel, but both trucks have the famous GM dash rattle. Anyone find a cure for that?

Cold sweat- disassemble dash and take top shell off, it is a piece up by the left defroster, you should see/hear the rattling

Ive got an 08 3500 dually with 24inch diesel wheels, 118kg i was getting 11.5-13 mpg around town and 15- 17 on hwy, i put a Dpf delete with mbrp pipe, and a small progrommer just to override the cpu, my milege around town went to 13.5-15.8. on hwy 18-21 much better power and milege, and love it. oh and its a duramax!

Mine is an 07 LBZ GMC 2500 ECSB SLE 4x4. Picked it up in Lapeer. Well optioned, and mint with 100k on it. Looked at a couple before I found this one, but the deals are out there if you look around.

Kid, did your brother ever sell his?

Thanks
-Rob