Bought one just a year ago and had the exact thought process you do.
Don't want "new", gotta be 4 door 3/4 ton or better, diesels are sweet but do I really need one etc etc...
Ended up with an '09 Chevy 3/4 ton, 4 door with the 6.0 gas V8. Man I couldn't be happier!
It was 3 yrs old with 90,000 miles (mostly highway as far as I could tell), got it for $22,000. Closest thing to it I could find in a diesel in my neck of the woods (same year, size, mileage etc...) was $30,000 or more!
4 door cab has plenty of room and 2 pc back bench seat folds up for extra room back there.
I didn't get to pull with it much til this summer. Went campin' with my dad and took my in-laws new camper ... 9,000 lbs. Got some pretty steep uphill switch-backs to navigate and it pulled awesome! Dad was following with his '98 Cummins and camper. He was super impressed, got him sold on buyin a newer gas pickup when his wears out. Coming home from that trip we took a backroad with some dang steep, narrow downhill switchbacks. The transmission is amazing, not an Allison, but it did awesome! Put it in 1st gear with the "tow/haul" on and it held to 20 mph for 4 miles of steep, steep highway. Only touched the brakes once, no joke... I was tickled pink.
Also came with the tow-package, integrated trailer-brake controller etc... works great
Gas mileage was as expected - 15 or so avg (not pulling). I did get 18 on one trip to Salt Lake City but it's mostly downhill and I was really babyin' it. 10-12 mpg with a light load and less than that towing 8,000+ lbs. But I was ready for this so no biggie...
Low... ride... -er... Might look into bigger tires/ crank up the torsion bars or somethin... unless you like huggin' the ground
Mine's the basic LT model with the black rubber/plastic floor instead of carpet. It cleans easy but sometimes I wonder if it isn't just a cheap cop-out on their part.
One other thing:
If you don't mind the bad gas mileage, look into the older (like '07-ish) chevy 1-ton gas pickups. They've got an 8.1 Liter V8 with a genuine Allison tranny, I believe. My father-in-law ran one for work the last 5 years (company bought the gas of course), he LOVED it. I mean LOVED it... They just took it from him this year and gave him a '13-6.0L chev and you'd have thought they castrated him to hear him talk ha ha
He pulled snowcats and all sorts of stuff all over the place with that 8.1... uphill and down... never an issue. Just FYI...