Nozzle heat problem with original Ender 3 (sort of)

First, apologies if I have done something wrong on this forum. I am a newbie here and have never posted here before. I have an original ender 3 which I have been upgrading. I put on a metal extruder (no problems) and a glass bed (no problems). Then I put on a CR Touch bed leveler and replaced the original main board with a 4.2.7 quiet mainboard and downloaded and installed the correct (I hope) firmware for the mainboard and the CR Touch. I then got the ‘great’ idea of changing from a Bowden tube set up for a direct drive extruder. Way too many upgrades in a very short period of time.
The problem now is the nozzle heat. If, for instance, I set the nozzle heat for 200 degrees, it will heat to about 190 and then drop back to about 188 and then fluctuate between 188-191, eventually shutting down and telling me I need to reset. No matter where I set the temperature, it will do the same thing. I have replaced the heater and the thermistor and the same thing occurs. I have also replaced the mainboard again thinking that maybe the first one was defective. NO Change. I also wired in the old nozzle with its original heater and thermistor and again same problem. It would seem then that the problem must be in the software (I’m guessing) or the mainboard (two different 4.2.7 mainboards, possible but seems not likely). HELP! Where do I go from here?

Did you run a PID tune?