1996 jeep cherokee 4.0l long crank before start?

im dealing with a 1996 jeep cherokee 4.0 all-wheel drive. my sisters vehicle. it has a long crank time before the engine starts up. approximately 10 to 15secs. i hooked up my scan tool and checked crank sensor and it was fine. has distributor i checked the cap all is good. pulled distributor out and checked the distributor shaft gear for wear and it was fine. ohmed all the plug wires to be sure they were right ohms for the 4.0l checked plugs looked to be worn replaced the plugs with plugs from chrysler gaped them to proper spec. fuel flow and pressure is great to the fuel rail. what im thinking is a possible weak coil but not 100% sure. any ideas? anybody see this before? looking for chrysler/jeep techs. or anybody that might know. im a certified ford tech looking for some help. thank you, shane