i am wanting to know how hard its going to be to swap a 3.9 to a 5.9. i am buying a 5.9 off a friend for $400 and it comes with ecu, wiring harness, etc. Thanks

 

Swapping the engine will be very easy if it comes with all that! Just make sure its an OBDI ('95 and older) computer and harness or you'll have a huge project on your hands. The 5.9 is externally identical to the 5.2, which is a factory engine for our trucks, and the motor mounts from the 3.9 should work on the 5.9, so its just a matter of plug and play.

You need to consider what to do about your transmission though. If your truck is an automatic, you have the 42rh which won't put up with that motor for long. You'll either need to rebuild it with performance clutches, torque converter and shift kit, or look for a 46rh to swap (also a direct swap). If your truck is a 5 speed you have the AX-15, which will probably last even less time than the 42rh. For the 5.9, you'll want to look for a NV3500 or preferrably an NV4500 (which requires a body lift to clear the transmission tunnel).

 

it is out of a 96 or 99 and i have a automatic trans but i figured i would have to find a new tranny or have mine built