OK, now I have more information.
The canned tow tune is probably pretty good for your needs. I'm sure Bill can "tweak" it into a custom tune, but you should talk to him about it. Possibly, due to your gears, there may be some changes that will help. That's a pretty big load you'll have back there.
More beneficial than a suspension kit, in my humble opinion, would be a good, load distributing, anti-sway trailer hitch. Mine is an "Equal-I-Zer" hitch:
http://www.equalizerhitch.com/ Anybody have different thoughts?
I'd definitely use the canned tow tune to tow, and I found it to be a pretty good all-around tune too, before I got my custom tow and non-tow tunes. It does more than just firm up the shifts. It changes the fueling strategy and puts more "oomph" in the low end.
DO NOT use the 91+ tune when towing! That's too much weight for a performance tune. But, if you wanted to use high test gas, Bill could write you a 91+ octane tow tune.
The Level 1 tune is something you could use when not towing. It firms up the shifts, and possibly changes the shift points, but it doesn't do much else. I'd have it replaced with a good custom 87 octane performance tune.
I think, with the load you will be pulling, you'll appreciate being able to monitor the transmission fluid temperature and the cylinder head temperature. Even with the cooler, I think you'll be surprised at how quickly the TFT can rise when climbing a hill.
- Jack