Personally, I find the Avalanche less useful than the Suburban, unless you plan on carrying a lot of tall objects that require an open area in back. The payload area is a little bit narrower than a regular pickup. So if you're needing the cargo area for wider things, this may not be the ticket.
The mid-gate is a nice, but kinda a novelty thing personally. And I recall on first gens, some people having sealing issues when putting it back in place. Not sure if those types of things were fixed by the second gens as I was out of service by then. I've looked at 1st gen GMT800's because in 3/4-ton, you can get the 8.1 Big Block. But I keep running into the issue that on weekends, I usually have both kids and a big 100lb dog with me, and an Avalanche isn't the most suitable for all that. It'd be fine in the nice months, but come winter... In the Suburban, the kids get the 2nd row, and he's got plenty of room in the cargo area. But that's my usage, so...
Otherwise, it is a 1/2-ton GMT900 truck. Same engines, drivetrains, suspension, etc, as other GMT900 1/2-ton trucks. They're all stout GM GenIV small blocks, the same as generation of engines as the LS2's and LS7's. These three 5.3's DO NOT have Displacement on Demand (called "Active Fuel Management" or AFM, in GM speak), which was known to have high oil consumption due to the lifters and their actuation of the DOD feature. There WAS a 6.0L V8 available also, RPO L76... I.E. the same engine from the G8's. This one DOES have AFM/DOD and has had issues with high oil consumption due to that AFM/DOD.
The trans is a 4L60/65E. Not the strongest in the tool shop, but as long as you don't start modding the shit out the truck, removing torque management, increasing line pressure, shift points, etc, etc, it should last with regular maintenance.