[theastronaut]

A 5.3 lacks the torque needed to move a heavy truck, you'd need 4.56 or numerically higher gears to get the rpm up in the range where it makes power. I swapped one into a '51 GMC that had 3.73 gears and it was just ok. We have one in a 2010 Tahoe and it sucks when empty, and struggles to pull a trailer. I wouldn't consider an LS swap in a truck unless its a 6.0 or 6.2.

Our '79 C30 with a mildly built truck 454 (peanut port heads) and NV4500 will spin the tires in second just rolling into it and pulls a trailer really well. Look up Richard Holdener on youtube, he has a lot of dyno tests with junkyard 454s to get an idea of what can be done with one easily and inexpensively.