2001 F-150 Skipping

I have a 2001 F150 SuperCrew that is skipping periodically when the engine is put under a slight strain. The engine light will not come on to tell me what the problem is. I had it in the garage and had the transmission serviced, fuel filter changed, etc but they told me they couldn't determine the problem until the engine light came on. I have also changed 6 of the 8 spark plugs (the last two on the back of the driver's side are nearly impossible to get to). The plugs I replaced look okay. Of course this engine doesn't have plug wires so changing them isn't an option. Note: Engine is the short block V8. I'm at wits end...someone please help!

Replace the other 2 plugs. Also look closely at the coil boots to see if there is any sign of arcing, usually a small white spot. Or to see if the bottom of any boots are cracked.

Make sure to change those plugs cold, otherwise you'll possibly have one blow out. the first sign is an exhaust leak sound, such as a mild ticking. Number four was the one that let loose on me, only a $1500 repair job.