Car problems

so my car has been having issues lately. It wants to hesitate at lights and sometimes shudders when I am at constant speed.

So not being a slacker when it comes to my car I have already taken some measure to fix this, and it has gotten better. At least my car isn't stalling at lights anymore. But some of the issues are still there, so to any mechanic types who happen to come across this today:

1989 Chevy corsica
51,200 mi
4 cyl

I have already done oil change with new air filter, new gas filter, fuel injector treatment. I have on my to do list new spark plugs, and new pcv.

Any other simple things that it could be? I hate to think it could be a fuel pump, or anything major, especially at that low a mileage.

Anyway, just a puzzle that's been shuddering at me for a few weeks.