[SS1156]

I have a 99 GMC Sonoma with the Vortec 4.3L and a 4L60E. This thing gets terrible gas mileage which is common for the 4.3L. I love the truck, it's got the ZQ8 suspension, low miles and was a local one owner truck. The Carfax was clean and after I carefully inspected it I could not find any paint work done to the truck. I would like to drop in a mildly modified LS style motor. I was thinking maybe an LS1 or LS2 with a cam and intake. I definitely want to run efi. Has anyone ever heard of this swap? I would also like to run a single 4" exhaust. Please guys... any info or insight would be greatly appreciated.