Yamaha DTXpress/DTXplorer/DTXtreme

Hi,

I just got my DTXpress III about a month and a half ago and I'm having some 
difficulty playing certain rhythmns...
If I play a sort of roll (well, a very slow roll) on the low tom (a sound 
with medium short decay) and play occasional kicks the kick KEEPS CUTTING 
OUT!! There is no specific rejection on the kick from any other trigger, nor 
is there any self-rejection.  Is this a problem with polyphony??? Is there 
no way around it??? I've also noticed ride cymbals cutting out ALL THE TIME 
just playing the cymbal.

I'd really appreciate any help you guys can give me.  Has anybody 
experienced this kind of thing at all?  I've heard of kick triggers failing 
after lots of use but it has only been played lightly and plays absolutely 
fine with MOST rhythmns.
Cheers,

Matt