Do you rotate the filters? TriX filters do allow quite a bit of water flow, but they do a great job of filtering out small particles over time, resulting in them clogging more.
If you don't move the main filter off the circ pump standpipe every once in a while you can run into that issue of the heater shutting off.
Also, when you clean the filter, do you hose it out? spray filter cleaner on it? Soak it in a degreaser?
I'm willing to bet just rotating your filters will solve your issue.