I looked at an avalance when I was in the market and there's no way your fitting two ss in there. I bought a gmc z71 with the 5.3L ext cab regular box and theres JUST enough room to close the tailgate. I get all my gear/dog/wife with one bike comfortably to the track. It'll fit two bikes and equipment in the back and with the seats up in the cab all the gear will fit no problem. I don't think you can really go wrong with any of the full size trucks with a v8 (gm's 4. whatever is apparently no good though)