of course i could be a devils advocate here and if youre just after torque..... you could always swap a 4-53T into the bay. or, if youre really nuts, find an aluminum block 6v53T military Detroit Diesel. Throw a 5 speed spicer manual behind it, and youve got 700+ lbsft of torque. and sweet mary mother of god if youve ever heard one of those spool up to max rpm.... and you could even jake brake it for going down hill......
course im just a diesel nut... i LOVE my 6.2L, and have been inspired by the heath performance diesel 300hp 6.5TD. if only i had the money to act on such inspiration