why does my tach needle jump around when @WOT

[LX XLR8R]

i have a 5" monstertach that is wired into the the coil right b4 the coil..its been working fine and seems to be very very accurate..i had just replaced my aged accel TFI moduel on the distrubter with a old stock one i had sitting around..the accel finnaly had enuff and quit on me..i used dielectric grease on the metel to metal surfaces...this was doing this even with the aceel TFI...what it basically does is at WOT the car will be at 5k and then the needle will drop to 3k then shoot back up within a split second..you can just barely feel it in the cars pulling..what would casue this??i mean it couldnt be a wire/plug/cap/rotor cuz they are after the coil..should i try swapping the coil with a stock one??the coil is accel also..im stumped..and BTW the my plugs are white??could this be because i have one of the bad pr0-m77 mass air meters(rich down low, lean up top, cuts out uptop)..does the mass air have any say with spark??i mean even if i was running really lean that wuold not casue the coil to skip a beet like that??im stumped..thanks in advanced

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1987 black notch(ex 4 banger)
DSS 306 w/ main support...Elderbrock 6028 heads..gt-40 intake..24# injectors...70 mm tb..77 pro-m...accel 300+..mac full legnth..tremec w/ pro5oh...full MAC exhaust,off road h-pipe,long tubes, catback...ron davis radiator..subframes, control arms...CFDF II..o yea holley FPR sucks..dont buy one..
AIM=onesillynotch