I have a 1993 Ford f150 xlt. It starts sporadically. I've changed the compressor. The starter. The ignition. The sensor and the cylinoid (spelt wrong) and changed the battery. What am I missing?

turns over and doesnt start or doesnt turn over all the time???

Its sounds slow and hesitant ...like an airplane before it finally catches on an starts.(sorry) a rmmm RMM RMM like the battery is dying sound. But the battery is new. And I've had it checked

Sounds like you changed out the major components of the starting system. Did you purchase a new starter or one rebuilt. Sometimes rebuilt items are bad out of the box. However, it sounds like you have a bad electrical connection somewhere. Check the voltage at the battery with an meter. Should be 12.5 volts. With the engine running check voltage again. Should be around 14.5 with alternator. Question: Does the starting problem only happen with the engine is hot? If so check for overheating problems.