My Jeep start life as a 2.5 liter four cylinder gas engine with an AX5 transmission.  

Fast forward 9 years.  That is when I bought the Jeep.  It had a 4 inch lift kit and aluminum wheels with 33 inch tires.  

The vehicle was very underpowered.  So out came the 2.5 Liter and in went a Chevy 305 tune port engine from a 1988 Camaro Z28 along with an AX15 five speed transmission.  Okay, no more problem with a lack of power but the fuel economy was as bad as the original 2.5 liter.

So it was back to the drawing board.  I pulled the tune port and installed a Cummins 4BT.  Now I have the best of both worlds.  I get great fuel economy and the power of a V-8.