allright the 5.0 trucks are RWD or AWD
To turn a RWD truck into a 4x4 you will have to replace the transmission
Look at the exhaust manifold on the drivers side. Missing any bolts? The front ones?
Look for exhaust leak around the exhaust manifold, black soot will be present.
Often the exhaust manifolds will come apart or lose a gasket
The 96 exhaust manifolds are welded together like patch work from the factory, and they have been known to develop leaks
Let us know what you find