1983 GMC Sierra Project

Hello,
I recently bought a K10 with a tired old 350 under the hood and I am being tempted to go with a 5.3 swap. I have a friend who has done this swap in his 82 Trans Am, but I wanted to get some opinions from guys who have done a truck like mine. I intend on using this truck for pleasure and the occasional haul, so I want good power but also good mpg's. All info and suggestions are appreciated, Thanks :)

A 5.3 swap can help you have good power and 18-20mpg at best, but the cost isn't super cheap.