RonInJoliet, you nailed it. I used the RS/GRE 800 gain duck and while it does show stronger signals on the S-meter I have found the stock 396XT duck does much better on the simulcast system here. My suspicion is that while the RS/GRE 800 duck provides gain of the desired signal it also amplifies interference from the dredded NEXTEL sites and any multipath issues. That's the downside of gain antennas - they boost desired and undesired signals in the band. The stock duck is helically wound, or a curly round "spring-like" wire, so I think it's better at receiving signals that come to the antenna in different polarizations - like multipath digital stuff. On simulcast stuff the stock duck is much better. On stand alone, IR sites that aren't simulcast, the RS/GRE 800 duck can deliver a stronger signal by one to three bars.
I also tried a 1/4 wave stubby (3" long) and it did better than the RS/GRE duck on P25 simulcast stuff, but I too was surprised at how well the stock duck works on 800.
Those are my theories, any one want to chime in?
BG..