Actually, 3/4 ton trucks and diesels in particular are stacking up like cord wood before a hard winter. Drive around and take a look then low ball the heck out of it. You might get surprised.
I have 73k on an 03 and it runs sweet. For the GM's don't get older than an 03. An 04 to 04.5 is better as there is a free injector replacement deal on them for 7 years 200k miles. Better is an 04.5+ with the LLY engine that has the externally accessable injectors.
I would almost bet that you may be able to walk off with a diesel truck cheaper than you think. Around here the dealer lots are chock a block full of trucks and SUV's and not a soul is looking at them. Good time to buy --> if you NEED one. Nasty time to sell if you only wanted one before!
jb
On edit - I've averaged 17.803 mpg since new with about 25k towing. Empty it gets 20-22. Best ever was 22.37. But I drive like a grey haired granny most of the time. Towing is 10-14 depending on load, wind, speed and temps. I normally tow just under 10k.