Do you have an inline fuse (big gold bastard in a clear case) or a breaker in your engine bay? If you got a fuse check that it isnt arcing in the terminals. You will find one or both ends of the fuse will have black or beaded spots on it.

I had this cutting out problem and had the amp sent away for repair but came back with an "OK" report. We finally found that the fuse in the engine bay was the problem.