TJ 98 is very strong car and have some minor heating issues in summer especially when leave unattended.
Change the thermostat as it might not be opening in time, Check the engine fan is working on both speed (regular and Hi when car overheat). Check AC fan is working fine. See radiator isn't blocked or clogged with rust, if it is get the radiator core cleaning done.
What else, there is nothing much apart from above said points. Make sure all are are good to go and hopefully car wont heat up again.