You have one very strong auto box, if it is the A442F. Give it some good synthetic Dexron 3 fluid to help it shift smoothly. For me, the difference when changing from mineral to synthetic was very noticeable.
Anything can be done - more or less - but it's not straight forward.
The 4 speed has one Engine ECU and one Transmission ECU.
The 5 speed has a combined engine and trans ECU.
The wiring is different, and different signals and plugs for the transmission.
The instruments are different, with...