It might be helpful to know a few of your settings.
How many frequencies are in the list?........Is 170.5125 one of them?
Multi-Site: Off / Roam / Stat ?
Next time you're in the dead zone, you might try pulling off the road and manually key in:
TUNE 170.5125 ENT
You'll then be looking directly at the Independence/Massman control channel.
You can check your signal strength and decode %.
If decode % is poor, try applying or removing attenuation using the ATT key to find out which results in a higher decode %.
The WACN, System ID, RFSS, and Site number will not be displayed.
If everything looks ok, there is probably another setting in your Moswin setup that requires attention.
This site comes in full strength @ 99% decode from my house, and have had good results all the way up to Cameron, so I see no reason why it wouldn't work inside the area the site was designed to cover.