FM muffled issue stock 95 GM radio
 

The AM never worked in my 95 GM but FM and tape worked fine then FM developed this muffled issue and hardly works at all now. Since tape audio was fine I bought a refirb stock radio and to my surprise the issue of muffled FM and no AM remained when I plugged it in and it also showed my previous radio channel resets. I figured it must be in another module so I replaced the antenna isolator box in the trunk but that did not help. I spliced the new isolator is since removing the old one means removing the back seat and deck cover which I didn't want to take on. The only other piece I see is the amplifier box in the trunk but I can't believe the amp is storing the radio presets.
As I explained, the tape audio worked fine in the old (and new radio) so we sort of ruled out the amp. Is there any other place I can check for the source of the issue? I have money and time invested and really don't want to rip everything out to do aftermarket stereo.
Thanks.

Radio Issues
 

I can't help ya, Joe --
We never play the Radio or the Tape Player in the 95 MERC.