fuel filter?

that was my first thought (I replaced it a year ago).  I haven't checked it, but I'm thinking if it was the fuel filter the problem wouldn't consistantly go away after 15 -20 minutes.  I've been reading the internet and have found some other possibilities, EGR Valve or Modulator, Charcoal canister, or moisture in the distributor cap.  What do you think?

I'd replace it again.  You could have got some dirty fuel.  Fuel filters are inexpensive.

It could be some of the other things you mentioned also.  My cousins 87 sammy did the same thing yours is doing.  Ran like crap in the mornings, and ran better after it warmed up.  Changed the filter and it ran better for a few days and started doing it again.  He had alot of crap in his fuel tank, ended up having to drop the tank and boil it.  Problem solved.

It could be too many things. It sounds like you've not replaced the normal tuneup stuff that's all probably overdue, so it's virtually impossible to help you diagnose this. Could be plugs, wires, disty cap, rotor, fuel filter, carb cleanup, air filter, valve adjustment and so on.