I think the easiest way if it can be read from the OBDII port (which I'm almost 99% certain it can) would be to buy the Aeroforce Interceptor.
I'm thinking if a 2002 Ford Ranger can read the trans temp, our WJs will be fine too. See linky to
It can read trans temp from the sensor in the valve body of the tranny without drilling holes to fit sensors in the pan etc. I'm going to pick up one soon as it will be really useful anyway, just need to make up a pillar pod up first.