I'm a torque converter newbie, someone school me here. I have a 08 Denali, and I've read the factory stall is in the 1400-1600RpM range.
I've also read these things tend to grenade, taking out the trans, so before that happens I wanna upgrade it.
What difference would I see if I went with a higher stall unit, say 1900-2200RpM range?
The above is a gross oversimplification, although it's also true.
I would not DREAM of going with an aftermarket 'higher stall unit' unless I was able to pay for one with at least 12 years worth of a stellar reputation.
They are out there, but I strongly suggest you do your research after you get several names like FTI, Yank, Circle D, Ultimate, or Vigilante.
The BEST torque converters, even with a higher stall, will behave similarly to ones with a lower stall speed at lower throttle angles.
In other words, it is possible to minimize (but not eliminate) the compromises Geotrash cited, at a cost.
What tends to 'grenade', is not the torque converter itself, so much as the torque converter's CLUTCH.
If your tune stays in permanent V8 mode, you have delayed the grenade going off by at least a few years.
In your situation I'd very seriously consider the 6L90E torque converter that GM coupled with the LGH DuraMax TurboDiesel V8 in the Chevy Express & GMC Savana 2500 & 3500 vans.