Have a 2000 Cherokee (4.0/Automatic) - just started having this problem. After sitting for a few hours, I can crank and crank and it won't start. As soon as I stop cranking and turn the key to "start" again it fires right up. It's got 148,000 miles, plugs look good. I couldn't find a fuel filter.

 

The fuel filter is in the tank. I'm having almost the same trouble with mine and it is also a 2000 model. I ordered a CPS, I will change it when it comes in and let you know if it worked.

 

One way check valve in your fuel pump is bad. Everytime you shut your Jeep off every bit of the fuel in the fuel line drains back into the tank....then when you go to start it your fuel pump has to pump the fuel all the way back up to the motor....hense your long cranking period everytime you go to start your Jeep. I had this happen to me and the only way to fix it is to replace the fuel pump.