[NLRS] FT290RII troubles

[Zack Widup]

Just curious if anyone has any suggestions for this rig which I use as
a microwave IF.

I started getting reports of very mushy/distorted voice on SSB a
couple years ago. People tell me it's almost unintelligible.  I've
done some tests with a couple other stations and it seems to be there
no matter what power level I'm running, with or without the amp
module.

On FM the voice is fine. I'm told FM sounds great.

CW is also fine. Power levels out are as expected in all modes.

Any ideas where to look to cure this?

73, Zack W9SZ