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Does the length on the antenna cable in the car make a difference?

Yes. And the type of cable, and the quality of cable, and the type/quality of antenna, and how well the connector plugs are made and connected.

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Is it just the nature of the digital beast that I go from what I'll call a HIFI sound to mono sound when the signal is starting to cut out?

No, it's the nature of the analog FM stereo beast.

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Will a better FM signal mean steady RDS flow or is that a different signal?

It is the same signal, but it won't guarantee a steady RDS flow. There is only one RDS station I know of in my local area, and even when I'm getting a fine signal from it, the RDS data is corrupted.

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Can RDS be turned off?

Yes. Switch to one of the info modes that doesn't show the RDS data characters. Also make sure that TA and AF are turned off, as those only work in the UK and I think in Europe.

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Lastly I noticed that the tuner always defaults to a screen that says no “AF information” if I was using a visual, any way to fix that?

I've heard of others getting that screen, it has never happened to me. Try setting to Info: Radio followed by Info:Transient followed by Visual: Your desired visual USING THE PLAYER'S MAIN MENU and then activate the Hijack "Restore DC/Car Visuals" feature. Do not press the Info button on the remote or use the knob press to cycle through info modes. See if the problem then goes away.
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Tony Fabris