02 Ford ZTS Electrical Problem

I have had numerous problems with my 02 Ford Focus ZTS lately. The lights on my dash and radio have been flickering, my a/c has been turning off and on, the radio will suddenly just shut off for seconds at a time, and the car will jerk radomly when I'm driving. The tachometer is also reving up when the is shifting gears. I have already taken it to the shop two times and got a new alternator, but it is still acting up. Can anyone tell me what is wrong with it?