It does take more power to turn 31's but your TJ should be able to do better than that.
Check the ATF level in your transmission to see if it's up where it should be. Being low on ATF can cause problems like that.
The engine MUST be running when checking the ATF level and it MUST be shifted into Neutral to get an accurate ATF level check. The transmission's dipstick comes out from under the firewall at the rear passenger side of the engine. Make sure the engine is actually running and the transmission is in Neutral (set the parking brake) while checking the dipstick.
If it's low on ATF, make sure to ONLY add ATF+4. If it doesn't say ATF+4 in big letters on the front of the bottle, it's not the right stuff. No, Mobil-1 ATF is not the right stuff.
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