My vote is for the older 8.1 and save the money. I have looked at both old (00-06) and new and while older, I don't think they're worse. In fact I find the materials (dash and switchgear especially) to be of higher quality in the older trucks. So many newer Subs have cracked dashes and the labels on the switches are all rubbed off. The 3/4 ton platform underneath did not change so both are still on the GMT800 platform, just with different bodies. The fuel mileage will be better on the newer one with the 6.0, but with 30k in your pocket I doubt that matters. Lastly your resale value on the older one will stay the same or increase, but will decrease substantially on the newer one. Good Luck!