I had a 3200 stall in my previous 2dr, it was about 4600lbs, was my daily and I drove it several time to NC from MA. No tune just a built trans, stall, intake and exhaust. Granted its a SBC but it still drove great as a daily and when you got on it, then you knew it was ready to roll.
A 2500 may be a bit small for such a heavy SUV. I think you'd be happier with a higher stall in the 3000/3200 range. Especially with the power adder.
Do you have experience with HP Tuners?
Did you buy a junkyard 80 and do work to it?
Is the Speartech a plug and play harness? I think it is.
How do you like the 3k stall? Is your Tahoe 2wd?