Liberty engines are notoriously unreliable. Based on the same architecture as the 4.7 it's no wonder. I am considering dropping a 3.9 Magnum engine and 5spd trans from a Dakota into a Liberty.
Since the 3.9 is a 5.2 missing 2 cylinders, most parts for the 5.2 work on the 3.9. Pistons, Rocker arms, and valves can all be upgraded fairly cheap, and a cam is readily available from Hughes.
I believe a decent 350HP build would also improve mileage over the stock engine bay bomb. Plus longevity would definately improve.
Anyone have experience with such a thing?