A few of the US Jeep sites speak of cracked flex plates. Mine has done 300k and there was no sign of cracking near the crank. I can confirm this as I had the trans out. I am not sure if the cracking is common in Jeeps with higher mileage than mine. IMO you would be best to spend 50 bucks and get it diagnosed by a trans specialist. My internet diagnosis on my trans cost me in excess of 2.5k by the time I finally got it sorted. Where as if I had it checked the cost would have be 300-400 bucks.
Regards A