GT2560 Rev B intermittent Temp control repost

[Stern5871]

Please excuse the repost from Products...
William was kind enough to suggest the MOSFET, but voltage to it is stable when printer works...

I have a MeCreator2 that seems to regulate extruder temperature when printing only when cooling down to reach its coded setpoint. On manual, i can select temperatures and extruder heats and stabilizes to that setpoint. When printing from gcode, setpoint temperatures are correctly displayed on LCD, but extruder will continously heat until maxtemp error. If i preheat the extruder above the gcode setpoint and print, the job begins when the extruder cools to the setpoint and progresses normally.
Troubleshhoting steps so far:
I have reflashed the firmware
Run print from SD card and via USB
Continuity checks from head to GT2560
Changed extrduer heater unit
Thanks for any advice!
software controls the temp fine when cooling to setpoint
Here is a dropbox link to a short video showing the issue
https://www.dropbox.com/s/xffr7tbze2qx6 ... 1.mp4?dl=0

[Stern5871]

Link to video (corrected)
viewtopic.php?f=18&t=60510