I have zero diesel experience so bare with me.
Pulled eng dipstick and oil was black.. Is that normal?
Going full throttle while cruising at abt 30 mph, tranny down shifted twice, then up shifted, then down shifted, then up shifted.
Are 6-speed Allisons supposed to act like that?

After abt 2 seconds of full throttle, I could feel a faint miss. Could this be just a fuel filter replacement?
The truck does not smoke at idle or at full throttle.

Does the truck have a tuner on it?
How many miles?

Diesel engine oil will be black, especially if it has a tuner on it.

No tuner.
100K miles.

I am no expert but my dad has similar truck and I am fairly sure if you go WOT it downshifts once (maybe twice) not sure why it down-up-down would happen normally. Also when his is in need of a fuel filter the power is down linearly , no perceivable miss, just less power .

Thx! That's what I needed to hear. I'd hate to spend $25k+ just to find out the eng/tranny is bad.

Any tips on what to watch out for when buying a LBZ equipped truck would be appreciated.

Nope - Great engine tranny package, fuel filters are regular maintenance with the duramax, and oil is always black regardless. Only downside if is a 3/4 ton ( depending on year ) is it is a rough riding truck' I would look into some better shocks if factory - I did the blistering 5100's and that helped out, put a load on it and it's great. Also, everything about diesels is more expensive - just a FYI !! Good luck !

Go to Diesel Place .com, this is a G.M. site and check out the forums. Your LBZ has its own section and they will answer all questions you can think of.

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Love my 07 classic LBZ 95K on it now. 3500 Srw CC Only issues I have had are front end things. And I am pretty sure that is because I have 20's and too wide tires.

But It LOOKS good lol

chitty pic

Thx for the link to Diesel Place. Lots of good stuff. The "10 Most Frequent Problems With an LBZ" thread was especially helpful.

I've heard abt the fuel filter situation between Chevy and Isuzu. Read a couple of threads that suggested adding aftermarket filters and lift pumps. Not sure if that is necessary or not for a LBZ.

A 2007 Classic LT3 LBZ is exactly what I'm looking for. The GMC equivalent (Sierra SLE??) is a pretty sharp looking truck too. Either would work. The search continues..

When my duramax would "bog down" under hard acceleration it meant it needed a fuel filter change......I got about 10K miles out of a delco factory filter after the low sulfur fuel came out.