Your truck carries out power very well. I see the Trailblazer ss guys really liking the Yank 245mm sstb3600 converter. Look into it or give Yank a call. For all out performance I have always thought the smaller 245mm converters were better, they seem to offer quicker revs and better 60' while still having great top end from being lighter... It also helps take some hit off the transmission by somewhat cushioning the shifts...

Are you doing any towing with the truck? If so then you might not want a bigger converter, if you are just hauling stuff in the bed then my vote is Yank sstb3600 or even the Yank sstb4000