That same block in the SRT-10, is actually quite capable of putting out double the horse it's rated at. The Cummins Deisels can also naturally do alot more due to their high torque and chip possibilities. But quit talking "MPG" and "Sport-Performance" all in the same discussion. Does you're engine burn fuel with a combustion system? Yes. So the rate at which you burn your fuel or how cheap your truck is/was, has nothing to do with buying a class of sport-truck (even diesel) that does the quarter-mile the quickest, carrying at least 6 passengers, and towing a load. Not that people race trucks in that fasion. But my money's on Dodge. Super-charge the hell out of your Tundra, the domestics will still top it in power.
All the same, the current 5.7L Tundra iForce is only (barely) competing with Dodge's emission-choked small-block Hemi 5.7L. The 2009's are rumored to contain the 6.1L and 6.4L Hemi's. 425 HP and over 550 HP.
(Stock, un-modified).