Hot End shuts down during print and then heats up causing Underextruding  

Hot End shuts down during print and then heats up causing Underextruding

I have a production print that I have run dozens of times on this machine. Older I3 that has been extremely consistent. Recently it started underextruding and I thought the issue was a clogged nozzle so I did several cold pulls. Everything seemed good. Printed first layer fine and I walked away, and when I came back the underextruding problem again. So this time I changed the nozzle. Reset the first layer height and restarted the print. About 10 min into the first layer I noticed that the hot end temp temp had dropped to 80C and the temp was rising. I wiggled the power/control cables and I did not see any changes in the thermistor temp or any glitching on the display. 

I do not think that the thermistor or the heater cartridge are the issue (though they may be). I am wondering if it is a temp control issue on the main board but I do not know (total guess).

Any thoughts on how to fix or diagnose this issue? 

Thanks for any help!