If you don't regear, you may not be able to go over 55. On our 94 YJ, we had 33x12.50's with the stock gears and every time we'd go on an overpass it would slow down. Poor little 2.5l - we really pushed it. Even with the 4.2l though, I think you'd have serious power problems on the highway.
BTW, on the 93 YJ, stock is 3.07 but I'm not sure about an 89.
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