Look on your axle's differential cover where you'll find a small tag bolted between two bolts on the left-hand side of the cover. Your axle's ratio will be embossed into it, though take a flashlight and a rag with you since it's hard to read and it's likely covered with dirt.
It'll either have 4.11 (or 4.10 depending on which axle you look at) or 3.73 (or 3.74 again depending on which axle) embossed into it.
This is just to double-check what you have now.
With your 3-speed automatic, it's quite possible you have a 3.73 and not a 4.11 ratio. At any event, 4.88 is too low for the 3-speed automatic like you have. I'd go no lower than 4.56 (and 4.88 is a lower
ratio than 4.56 is) for 33" tires as you don't want your engine RPMs too high.