I have a 120/240 volt, 200 amp panel, recently my lights have begun to dim when the frig compressor or sump pump kicks in, also my micro wave seems to have lost some power, I have checked voltage on A phase and B phase, across A phase and B phase and from nuetral/ ground to each A phase and B phase, when panel has minimal load A phase shows 118.6 volt and B phase shows 126.5 volts, 6.1 amp on A phase and 3.8 on B phase, I also hecked voltage on primary side of microwave breaker which shows 126.5 while microwave is off but bogs down to 96 volt when it is running, at first I thought that was voltage drop but how could it be at the beginning of the circuit, so is why I think that may be the first clue toward this problem, I have checked all connection to be sure they are tight including the main 4/0 service conductor and I have change the sump pump breaker from A phase to B phase and change the receptical from gfci to straight non gfci protected, and just for xhits and giggkes check continuity from nuetral to ground, question, what the heck is going on with the lights dimming, I wired this house personally and am a master electrician, the sump is on a dedicated circuit, the microwave as well (#12-2 wire, 20amp breaker) sump 14-2 wire, 15 amp dedicated), could it be a deterorating underground neutral or phase, hopefully not ! Bad main breaker ? Im starting to get a little worried need help please.

Not sure... but what you're describing sounds like job I saw a while back where the service neutral was loose...
The symptom is the drop in voltage under load on one of the phase legs with a relative equal increase on the other...
If you can take more voltage measurements without and under load as close to the supply or utility connection as you can...

I think you may have a loose Hot or Neutral.
Measure the voltage at the Microwave Breakers Hot, and the Neutral Bar while the Microwave is running, and compare to the voltage at the Microwave outlet, if noticeably lower, you have a loose connection.

I would also measure between the microwaves Hot and another circuits Neutral to help determine if you have a bad Neutral or Hot Connection between the Panel and the outlet.