First, the only mod to my 2005 5.4 is a Gryphon. I drive the same route to work every day. It's a country road and I drive it at about 60MPH. 11 miles into the trip is a stop sign at which I make a right hand turn. I use the cruise control without issue up to this point. After the stop and right turn, I accelerate to a little over 30 MPH and then hit the resume button to engage the cruise and bring the truck back to highway speed. The cruise engages and the truck starts to accelerate. After about 4 seconds, the cruise disengages. The dash light goes off and I have to hit resume again. The cruise engages again and I don't have any more problems.
The really weird thing is, this only happens at that specific corner. It's happened 4 times on my way to work and twice on my way home recently. I've used the cruise extensively, including to accelerate up to highway speed from ~30MPH in many other places, and never had an issue. It's like that stop sign and turn out in the country is in the Twilight Zone.... There is a graveyard right there, lol. Anyone have any idea what to check? I'm not hitting the brake. In fact, the last time it happened I had hooked my foot under the brake pedal to pull it up to eliminate that possibility.
Do you have center console shifter? If so, can you put into gear with engine running without putting foot on brake? If you can put into gear with foot off brake, most likely you have a bad shift interlock with a burned out resistor in interlock. Will cause cruise control symptoms you describe intermittent to complete fail of cruise control. Interlock is inside center console on driver side attached to shifter. Replace interlock or if you can soider well replace resistor. Search form for shift interlock solenoid on what resistor to replace and or YouTube I think its video 17 will show bad resistor in shift interlock solenoid. The dealership calls it I believe shift actuator assembly.
I think I narrowed this down to my Edge programmer. If I apply more than 1/3 throttle from a stop, the problem happens every time. Less than 1/3, and it never happens. Since applying the Edge tune, the cruise control has acted different. It accelerates to 2MPH past the set point and then settles back to the set point when using the accel or resume function. It never did that on the stick tune. I'll have to set it back to stock to test my theory.
Something to check that I ran into before was the anti lock brakes kicking out cruise control the tone ring had a crack in it and it would kick whenever doing a turn under acceleration it was on a dodge mind you buy you never know it may be like that on the ford.