Amp protection?

Okay, so I installed a Rockford T1 12 in a customers car hooked up to a kenwood 9102d amp.  Sounded good but the amp would always overheat and go into protection.  I heard from a few people, as I had not worked with the new amps, that they were big piles of poo.  So I swapped it with the Alpine MRD-M605, played it for almost 25 min at near full volume and not cutting out or going into protection, but the customer didnt like that it was not as loud as the kenwood so I swapped that one for the Alpine pdx 1000.  Again, played for 20 min. and no protection, customer comes back today saying it is turning off again.  Its a 2006 dodge  magnum with the factory Boston system.  I used a loc tapped in at the rear speakers and got my turn on from the ignition wire.  Everything else is normal.  Somebody please tell me I'm not nuts and this guy is messing around with the settings or something.

Check all the connections...Ground? Low voltage? I've had a kenwood 9102D amp hooked up at 1 ohm (yes i know its not rated at 1 ohm stable but what the hell you know) to 2 kicker 15 inch L7's and it pounded real hard...I have a 98 explorer with leather and it got to the point where my back started to itch from the vibrations being so strong. Yes it cut out for a couple seconds sometimes while we were adjusting the gain but it just came right back on at full throttle. Personally, in my experience with kenwood amps, I think they are very good for the price and very durable. They can take a beating. They'll get hot but I've never had one go into protect mode. Got rid of that setup cuz of no trunk space and now running 2 12 inch type r's.

I know all my connections are good.  The battery in that car is like four feet away and I sanded away the paint for a bare metal ground.  I have never had problems with kenwood amps before either but supposedly these ones have problems.  The guy is coming back in on tuesday for a R&R and I want to have some ideas for what to check.