We tow a 165 thats 3,500 dry with a V6 Envoy (same as a Trailblazer) and use a WDH and sway bar. It tows ok but struggles on hills not to mention the mpg's are in the hole. I dont think I would want to tow anything bigger with my Envoy even though its may be rated higher than what I tow, just starting to feel a bit much for the mid size TV. Again I personally wouldnt go bigger than what you have now. Oh, got a tranny cooler installed on your trail blazer?
*Currently trailer-less but shopping
07' GMC Envoy w/ P2 controller (current TV)
88' Chevy K5 Blazer (soon-to-be TV)
74' VW Superbeetle (1303)