Has anyone replaced a Vortec 5.7L with the newer 8.1L ??

Just looking for options I have a 1999 Chevy 2500HD "classic" and it only has 50k miles and is an awesome truck but just never had alot of power. I Now have 37" tires on it but even with the stock 245-75/16's it would not do much. 4L80E trans and 3.73 gears truck has always been in the 10-12 MPG range - 8 if I am pulling a car hauler or small trailer.

Any ideas or suggestions would be great , thought about a FI 502 crate motor but I do not have $12,000 just laying around but I have seen some 8.1L low mileage motors with ECM's going for $1200-$1500.

 

Since you have the 80E trans I would go ahead and do it. You will probably get the same amount of gas mileage but guarantee you it wont struggle while towing.