It al depends on how much $$$$ you have to spend, what is wrong w/current motor, and how much of the work you can do yourself.

If you have the money to do a 3.4 swap either yourself/pay someone, it would be the best way to go for the heavy Runner.

If funds are low/rebuild the current motor.

If we know the current motor/tranny set-up we can give you better detailed opinions.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed