if you want to run your CURRENT 33's, you have to have a 15" rim, obviously.
if you want a tire that is 33" tall that fits a larger rim, you could run a 305/45/22, thats a 22" rim...or a 305/35/24, that'll impress the guys on mtv cribs. those tires are both about 33" in diameter. heck, you could even run a 305/30/26 (yes, they make them)..thats only a little over 33" and gives you 26" rims.
in case you cant tell...the limiting factor here is not the tires, its the wheels. the real question should have been "whats the largest rim made with the rangers 5x4.5" bolt pattern?", or "what size tire do i need to still have a 33" diameter for a 17" or 18" wheel?".
while i cant answer the former, the latter is easy:
17" wheel: a 305/65/17 is 32.6" tall and 12" wide.
18" wheel: a 305/60/18 is 32.4" tall and 12" wide.