Agree with the LS Turbo. My current setup is a 98 Sub 2500 with a twin turbo LS6 from a Cadillac CTS-V backed by a Hughes built 4L80E. Small turbos and a torque biased cam delivers boosted power starting at 2000 rpm with a very flat torque curve. Has been very reliable and with the aluminum block is so much lighter than the factory big block. Expensive build though. Lots of tuning effort required. Before that I built a turbo charged 454 in a 98 sub 2500. Used a remote mounted turbo from a dodge cummins. That made great power too, was much less expensive and arguably more durable. The turbo solves the sluggish feel of the 454. Any boosted solution will require premium fuel so that is another consideration.
Thanks for the info! Some of the places that I end up with the truck might not have premium fuel. I didn't think that through... I will probably end up with an 8.1 because of that.