Won't start some of the time

I have a 1994 explorer limited with the 4.0 engine and 165000 miles. Last year it got to where it would turn over but wouldn't start at times but would start after waiting a little while. Then it got to where it would crank but wouldn't start at all. I replaced the coil pack and plug wires, cleaned the maf sensor and it solved the problem. Now it is starting to come back but very rarely but will start after waiting the same amount of time as before. The maf was cleaned again before the problem returned. What else can I look at that could be causing this problem? If it maters the trans was rebuilt a few months before the problem started.