My 2001 5.4 F150 has 145,000 miles always runs great, fuel pump I replaced 8 years ago I've replaced spark plugs at 100,000 miles. For quite a while when I'm driving towing my work trailer 1200 lbs you can be going up hill and no buck but if you back off throttle and slowly push pedal it bucks once , I've had cars before and either a bad plug or plug wire going up hill it will miss, but this is different its like throttle sensor is bad? any ideas?

 

Did you do the ignition coils or boots/springs?

 

No! I thought if a coil went out you would get a check light, and it would miss under load continuously

 

I would try that.
Have you cleaned the throttle body and MAF?
Check engine light? Flashing or stable?

 

No I have not did either, can you explain? Clean throttle body pull air mass and clean?