asap used japan motors and a/t in houston tells me that you can install a 4 speed a/t into a base prizm with a/t. but it must come from japan. the domestic 4 speed will not work.it cost $395. and they have it in stock.i,m not a mechanic,but i guess you would have to do something with the selector in the car? if anyone tackles this job ,please keep us posted on the results.

well i just swapped the 4age 20 valve into my prism with 4 speed auto tranny so yes do it