FIX or BUY NEW?

From what your saying I feel the need to ask if the radio was tuned and peaked. If it was, and drawing a high watt, that might be your problem also. Don't know what size amp fuse your putting in there, but that is something to think about.
someone correct me if i'm wrong about this but I thought that there was a certain truck that use to have reverse polarity on the cb hook ups but I can't remember which one. But then again, if you hooked it up backwards or on a reverse polarity hook up and blew that diode that everyone else is talking about the radio wouldn't even turn on. There are numerous things that it could be, but I personally would check the cheaper things before you go out and spend money on a new radio . Hope this helps.