Tom:

I had a similar situation, finally traced it to a bad coax jumper.  I havent 
torn the jumper down yet, but it wasn't a completely broken connection, just 
weak I think.
suddenly, receive sensitivity would drop off, and auto tuner acted 
strangely.
I could shut the rig down, or sometimes bang on or wiggle an antenna switch 
and things would come back.
Tried changing the switch, removing and replacing with a barrel, finally in 
desparation, I replaced the jumper to the rig.  all troubles vanished, and 
have been gone for six months.