Will the seats from a 1993 silverado fit into a 1995?
YES, The cabs are the same.
Will the transmission on a 1995 Chevrolet silverado extended cab fit a 1994 Chevrolet silverado stepside?
These will not bolt up, there is a different floor pan design, with help from an engineer they may be able to make alterations to the seat rails to make it fit though. The 2001 Celica seats are very comfortable. I may recommend finding some GT4 ST205 seats if you can't get the 2001 celica seats to bolt in