Another 5.7 vortec or swap to 5.3?

[68c10owner]

I`ve got a 97 GMC C1500 that has a 5.7 vortec with roughly 70k miles on it. It has started using oil and every since it over heated 2 yrs ago I`m sure its got a cracked head or heads. No coolant in oil but it uses coolant too. I dont have the time to pull it and rebuild my engine so I`m either going to do another vortec crate engine or do a 5.3 swap. This truck has always been down on power and gets terrible mileage compared to similar trucks. This truck is completely stock and will pretty much stay that way. Since it is already fuel injected how hard would it be to swap it over to the 5.3?