Hmmmm. Brian, I must say that I reckon the Uniden rep may be right. I note most responses below state to check coax line loss or multicoupler problems etc, but you say that non-trunked freqs work fine, only trunked freqs are screwey and even then the whip works fine on both. If you manually lock into a data channel, how does it sound? Is it scratchy or sounding distorted. Is there any low level hum or high level squeal? (you will have to connect headphones with decent freq response to check this out). Any of these symptoms will confuse the trunking decoder. Even better, see if any ID's flash whilst you are manually locked onto the data channel.
Oh, check for cell phone base tx noise. Especially if you have any digital cell phone tx towers in your area, they are very prominent and very irritating in the form of incessant buzzing which used to confuse the crap outta my 245 on 800MHz trunking.
The 780 is quite sensitive so it would be easy to overload the beast (mind you I have never used an 895 and most responses below seem to indicated the 895 is much more sensitive).
I reckon the key is desensitising of the front-end.
