Keven,
There are some communication frequencies that interfere with GPS signals. I forget which harmonic it is, but it somehow seems to drive the GPS wild. There is a little item called a "notch filter" which goes in the communications radio antenna cable which will usually prevent this interference. IFR GPS systems have to be tested at each of the frequencies known to cause problems before they can be certified for IFR use. Sometimes the tank circuit in the output of certain ELTs will cause similiar problems. I think this only causes interference when transmitting on a comm radio.
Check with a good avionics shop. They should be able to resolve the issue.
Ever coming to Richmond? Does Peyton still speak to skymaster people?
http://www.aircraftspruce.com/catalo...s/tednotch.php