Carb or timing. Disconnect and plug (on the carb side) the vacuum line to the vacuum advance can on the distributor. Test drive the car, and if the problem goes away, it's the cannister. You may lose power due to the lack of spark advance, but if the engine runs steady, you've found your bug. Also, remove the rotor and check the advance weights for freedom of movement, wear on the posts, etc.. If they seem to be sticking, spray them with WD-40.
If it's a carb problem, it's a bit more difficult to diagnose without knowing what carb is on it. The fuel filter does not sound at fault. If clogged, it will have an effect moreso at full throttle. Likewise, the transmission modulator should not produce this exact symptom, but I can't completely rule it out.
With a little more info, I may be able to pinpoint your problem. You can email me through the above link if I don't get back to you through this forum, as I sometimes go for days without checking in to this site.