I just purchased a 2000 Cherokee XJ with 124k miles on it and no service record but very little rust and it seems to run pretty solid. My question is: what are the most important things you would do right away to make it last another 100k miles? I spent 2k on it and have another 2k to put into it and I intend to keep it mostly stock.

 

On your '00 the cooling system would be your Number one priority. Your year has a crappy 0331 head on it that have the tendency of cracking when over heated. I would give the cooling system a complete flush and replace any if not all the cooling system parts if you have no idea of it's age. I would go through the radiator, hoses, rad cap, t-stat and one thing that many over look is the fan clutch. Besides the cooling system I would a complete change of all the fluids

 

Get you a manual (FSM,Haynes,Chilton,etc.) and start with a tune-up and routine maintenance.