i dont think wranglers came with 3.55's, at least i never seen it.
The 4 cylinders come with 4.10's or 3.73's. The 6's came with 3.73's, sometimes 4.10's and 3.07's.
my 4 cyl auto came with 3.73's.
My friend's yj (6 cyl, auto) came with 3.07's (SUCK!).
Normally there's a rectangular tag on the two side differental cover bolts that would say what gears are in it.
Some more info: It should have dana 30/35 axles, if you are lucky a dana 44 in the rear. Look for a stop sign like diff cover, that's the 44. It has the np231 t-case.
If you buy a wrangler, i will hate you, only cuz i want one again.
If you need any other info on wranglers, feel free to ask.