i got a 1991 caprice that shuts off when i drive, sometimes it start right back up and sometimes it dont, when its getting ready 2 shut off the lights dim and my power locks be moving up and down like crazy. i put a new altenator, starter, and battery i dont know what tha problem is

what kind of alternator did you put in?

if your idle is too low, and you put in a one wire alternator, you wont be making electricity until you rev the engine up to the alternators minimum speed.

try raising the idle a bit and see what happens.
it sounds like a definite electrical problem, but i'm guessing its alternator related

my caprice is not acting right

Welcome Aboard!

It's probably not an act. It likely has a genuine electrical problem.

If the '91 is a TBI as I suspect it is, raising the idle RPM is not an option. The target idle is controlled by the ECM and IAC. Changing the throttle stop minimum air position is not an acceptable way to increase idle RPM.

Check the alternator output directly at its output stud on the rear of the case. Set your meter for AC volts, and see if the AC component is over 0.2 V. That would be a sign of a failed rectifier in the replacement alternator.