Coolant system mystery

I have a 93 lumina 3.1 and it had a bad radiator, i got the leak fixed but now it still will shudder and die after a decent drive. it will even say low coolant. but the coolant level is fine. Is this a vacuum problem or something worse?

system probably has a air lock and needs to be bled

theres a switch in the overflow tank that turns the light on. try tapping the side of the tank with a screwdriver handle. if the doesn't work remove the tank and shake it a few times, then it will probably work fine.
good luck