My brother has a 1998 Jeep Cherokee XJ with the 4.0l engine and the AW4 transmission. We were off roading and he was trying to go up a hill when this began. In first gear, his jeep lurches forward when under load. It behaves as if you pushed in the clutch on a manual car and then dumped the clutch, causing the car to roll back then lurch forwards. This only occurs in first gear. If he accelerates gently, it's fine.
HIs fluid level is fine, it was just changed recently. The fluid before the change looked fine. This XJ seems to have been well maintained.
Could it be the first gear clutches? We don't know much about how automatic transmissions work so we're a little lost on this one. Any ideas or advice are appreciated.

Check the trans filter if it is loose or some had a gasket it can be a problem . the trans will not be able to pull the trans fluid on a hill

I known you're not on a trail or hill right now, but it might be worth next time trying to see if it does the same when you go 'manually', so keep it in 1-2 and see if the lurching disappears

He's going to drop the pan and check the trans filter and fluid.
We were wondering if the transmission overheated. He just has the stock transmission cooling system and with the 31 mud terrains he just put on, maybe it was too much for the transmission to handle. Is overheating the transmission a common issue?

The AW4 is prwtty robust but many installed an aux cooler to prevent trans overheating. Its a pretty straightforward thing to do and, together with clean fluid , prob the best protection against overheating issues.

We solved the problem. The transmission fluid filter had fallen off and the transmission couldn't get fluid. He reinstalled the filter and the problem disappeared.
Yes, you can make fun of us for being idiots lol!

Good to hear!
Doesn't make you idiots at all.
Thanks for coming back and inform how this was solved.