Just to be absolutely clear on this:

YES, there are certain problems that can happen with too many songs, but the problems you've just described are NOT caused by having too many songs as far as we know. Your problems are caused by something other than the number of songs.

Things to check right off the bat are here, here, and here.

The car-cutting out thing could just be a loose wire on the amplifier remote activator. The lockups and pauses on AC power could just be a bad AC power supply.