* AX-5: A 5-speed manual transmission. This was a very common option.
* AX-15: Another 5-speed manual transmission, also frequently found. There are subtle differences between the AX-5 and AX-15.
* 42RE: A 4-speed automatic transmission.
To know for certain which transmission is in a *specific* 2001 Jeep Wrangler, you need to check the vehicle's documentation (owner's manual, build sheet if available) or look at the transmission itself (although identifying transmissions can be tricky for someone not familiar with them). The information is also sometimes available on the vehicle's identification plate (VIN decoder sites may help, though accuracy isn't always guaranteed).
