Stuttering at 1500rpm, then fine...ignition or fuel?

Started the car after a few weeks. Run STABIL in my fuel when it sits for long periods. Car is idling odd, so I let it warm up for a few minutes, and take it for a spin. Car stutters at 1500rpm, then jumps up in rpm and is fine. I put it in park, and rev it up to 1500rpm...feels almost like its missing, then it jumps up in rpm quickly and all is well...
Fuel bad or fuel filter clogged? Ignition maybe?
318 small block, filters are all within a few months old, and all ignition was replaced last year...car runs perfectly most of the time yet this is odd.
Ideas?
thanks