sounds like when you stepped up the output, you eventually starved the amp, probably took a couple of hours of riding around playing hard for the battery voltage to drop low enough to shut it down. Are you using a deep cycle AGM as your primary battery, or a regular flooded starting battery? the AGM's are more efficeint, which is why they are used in higher powered systems. If you have a regular starting battery, or a combination of the two if you are running 2 batts, I bet your battery is going bad. Have you checked the resting voltage with the engine off to see if it is lower than it should be? Another thing to consider, once an amp shuts down, it is kinda like a breaker. Once tripped, it may not take as much abuse before the next time it trips.