[Kenwood] TM-742A & AD Owners Inquiry

[nj9k]

I have a TM-742A that has a 144 module problem, I think???  When I use
146.490 and
ragchew after a period of talking all of sudden my modulation fades to
nothing. After I
unkey the mike all the group lets me know about the fade away and gone.
I can change
bands and return and everything is normal again.  This only happens on
"HIGH POWER".

I connected a swr/power meter inline and it showed no loss of power but
yet the
deviation dwindles to nothing.

Has anybody ever had this symptom?  The 144 module is the middle layer
between a
220 module and a 440 module.  Heat? Mic? Power module? Deviation
component? OR
Gremlins?

Help!!!

Dick, NJ9K