[cal30_sniper]

I'd stay with the 454. The cummins is going to end up running you far more than 2k when you figure out all the odds and ends needed to put it in. It's the nickel and dime stuff that gets you every time. Plus the dang thing weighs far more than a 454, which is going to make it quite nose-heavy.

Keeping the 454, I'd look into 3.73 gears. An NV4500 swap shouldn't be too difficult either if you source the parts relatively cheap. That'll give you overdrive and much lower overall engine RPMs. That's the exact combo I'm running in my C20 Suburban. Headers and intake on that 454 really woke it up, and the NV4500 was just the connecting bit I needed to really get that torque to the ground. I just got through moving 8000+ lbs of stuff from TX to FL (including a dual axle trailer) and averaged 10.7mpg doing it on 32" all terrain tires. Haven't got mpg figures yet unloaded, but I'd be willing to bet I'm getting real close to the 15mpg mark. I was over 14 on occasion before the NV4500.

Best of luck, that's a great looking truck!