Ummmm - - Your stock head unit has pre-outs?
If not, you are probably using a line-out converter for your input to the amp, that won't be 1v....\
Unless it is a very good LOC, it can really really really really contribute to distortion and clipping which = protect mode.
I wouldn't assume that gain needs to be up, I would make sure that it is set properly. good thing you are getting that taken care of.
That is probably part of the problem. I am using a LO converter right now. Maybe it is clipping hard since it was only $35. I can get a new HU whenever I want but not sure what I want to get.
Checked stuff with dmm earlier just to see.
Final Ohm load was .9
Fulltilt voltage was 13.64 b4 it cut off.