1997 1998 1999 transmission differences? ford f150 2x4

hi im trying to get a transmission for a friend, he has a 1998 ford f150 2x4 i went to the pick n pulls and found all 1997 trans 2x4's on the part interchange it says 1998 2x4 only. what is the major difference from 97 and 98 transmission? the engine is 4.2. the trans lost 1 and 2 gears and has reverse. any help would be great thanks alot