My next-door neighbor has a 2005 GMC diesel with the Allison automatic (4-door shortbed looks like). It has 200,000 commuter miles on it.
Just back and forth to work. Never towed a thing. Are there "issues" I should be concerned with? Would you go for this truck (I'd use it to tow my Fountain 29 with twins on an aluminum trailer)?
It has leather, white, no dents or dings, polished wheels. I've never owned a diesel before and have only been a passenger.

The Duramax is a reliable engine and they are rated to go 300K miles before major overhaul with proper maint. I'd say if it was properly maintained, should be fine.

that all depends on the price

ya, 200 isnt really THAT much. but after that many miles stupid little things start to go... like window motors, steering bushings, shocks, rear end, etc etc. i would never buy anything with that many miles. well, i did actually, then i sold it. a LLY is a decent version of the dmax. but go for the LBZ (06-07) if you can. but they are all good. the LLY has been known for head gasket issues, nothing like the 6.oh ford though. the LB7 (01-04) have injector and head gasket issues, so dont buy an LB7 unless its had injectors done recently.

I had that truck in a 2003......went 170K miles before I traded it (got 8900 on trade for a new F150).

Issues from day one:
1. Water pump 106K miles
2. Wheel bearing at 132K miles (at that time we changed the brake pads for the first time also)
3. Injectors replaced under GM warranty (157K miles)
4. Gauge cluster started going haywire (160K miles). It would function, then the next start the needles would go all different directions (cheap fix just never did it)

Other than that, 3 sets of tires and two pairs of batteries in the 8 years I had it. Ford mechanic bought it and is still driving it (over 200K miles now). He told me he fixed the cluster (used one off ebay) and he stuck a used set of tires on it!

i seen 2007 one last week with 685000 untouched miles on it..besides the injectors..

Here is some math to make that guy cry......

685K miles @ 15 mph is 45,666 gallons of diesel......so at 3.50 a gallon that would be $159,831 in diesel fuel! OUCH!

I had a 05 like that for almost 5 years, never did anything to to other than 1 set of batteries and change oil...sold with mileage in the 50's though...truck did replace the LF hub/bearing, not a big deal at all...and did have aftermarket wheels/tires

Do some research on that year i was looking at an 03 Duramax and found out they had injector issues which cost $4-$5k to replace not sure if the one your looking at has the same injectors set up as the 03's but if they have not been replaced it is an expensive repair.

Probably OK….
I have a friend with an '06/'07 with over 200k, towing miles…. Still looks and runs good… He still runs a Edge tuner on it….
If it has had good history I wouldn't be too afraid… GEt it right because you won't get that much for it if you try to trade it though.
My '04.5 ply that I sold 2 years ago was great..