You can tow with the BDDL on performance or extreme, just watch your egt's.
As far as stacking with the TST, on my '03 the Tow setting with the TST on 4x4 is just nuts. I break the tires loose in 3rd gear with a plume of smoke. My stock clutch doesn't like it at all. Won't hold over 4th gear.
Tow setting seems to fuel harder on the bottom than extreme or performance, at least in my truck. TST takes care of the top more than adequately.
If I were to tow, I'd probably leave the downloader on stock, and run the TST at 2x2 or 3x3. The main thing is to watch your EGT's. They'll get up there quick with the stock turbo.
I can't wait for my new clutch!