I believe the last American made animated show to get a truly large season was Lilo & Stitch at 39 episodes (for the first season, S2 got 26 additional eps), and that was probably because it was intended to be on Disney's syndicated One Too block before it got axed and L&S was moved over to Disney Channel.
The odd things about syndication is that a lot of shows got 65 episode orders that built up over several seasons:
G.I. Joe: The two original 5 episode mini series, then a 55 episode addtion afterwards. (then 30 additional episodes, plus the movie)
Teeanage Mutant Ninja Turtles: The original 5 part mini, a 13 ep second season, and 47 episodes for it's 3rd year. (After that, it moved to CBS as well as got a 15 episode 4th syndicated season)