thoughts on a new (to me) GMC... 6.0 vs 6.6

[msgross]

ok, I know this isn't in the 99+ forum but we have the most traffic here, I can move it later if needed. My toyota camry (don't laugh) is slowly dying, it was free from the in-laws a few years ago so I sold the Ram to start on my 68.

anyway i'm leaning towards buying a truck but really want/need/told to keep it under $20K max (she'd be happier with $15K). If I wait another year I could go $25K or so but I don't know that I can wait that long.

I'm looking at our auto auction on Thursday for some crew cab diesels, slim chance to get one with under 100K for $20K though. And I found this truck for sale too... I don't really tow and only drive 15 miles to work so the 6.0L would work well considering MPG.

I must have a crew cab 4x4, other than that all options are open (except another HEMI)

I think I can get
1. '05 duramax crew diesel for about $21K+ w/100K
2. '07 1500 crew w/80K for $18K
3. truck below for $15K

I found this for $15,500 (might go down to under $15K)
has 3.73 gears per the PO
04 GMC Sierra 2500 Crewcab 4x4, shortbed, 6.0 liter, auto, 89,500 miles, cold air intake with K&N, loaded, On-Star, Bose stereo, power heated front seats, very nice leather int., tinted windows, tonneau cover, Rhino bed liner, like new tires, very clean in and out, runs great, all fluids just changed, no rust.