Anyone with experience towing with a Suburban

BurbMan makes some good points. To add a little:

I used Royal Purple MaxATF in the transmission (Dexron III equivalent). My friend now owns the truck, and it has 195k miles, and the transmission still functions/shifts perfectly.

I installed an HD gauge cluster in the Burb. The truck is already pre-wired, so once I plugged in the HD cluster, I had a functioning trans temp gauge. I don't like the tacked-on look of aftermarket stuff. The OEM cooler always was sufficient - the transmission was never more than 100° over the ambient temperature.

GM specifies full synthetic 75W90 for the rear axle. No need to use something different, just change it regularly. My interval was 15,000 miles whenever I'd take a long trip.

Your Autoride Burb does indeed have a self-leveling system. To quote from the link provided by BurbMan (03 manual, page 4-58):

The automatic level control rear suspension is available
on C/K 1500 vehicles and comes as a part of the
AutorideTM suspension.
This type of level control is fully automatic and will
provide a better leveled riding position as well as better
handling under a variety of passenger and loading
conditions. An air compressor connected to the rear
shocks will raise or lower the rear of the vehicle
to maintain proper vehicle height. The system is
activated when the ignition key is turned to RUN and
will automatically adjust vehicle height thereafter.
The system may exhaust (lower vehicle height) for up to
ten minutes after the ignition key has been turned off.
You may hear the air compressor operating when
the height is being adjusted.
If a self-equalizing hitch is being used, it is
recommended to allow the shocks to inflate, thereby
leveling the vehicle prior to adjusting the hitch.

The one caveat to the self-leveling suspension - there's no tipoff that you're overloading the rear axle because the truck isn't squatting.