93 DX - Random hesitation/power loss until wide open throttle

I recently bought a 93 DX with 150k miles on it. At random times (below 40 mph) it will begin to hesitate and the power will bog down. If I press on the gas more it sounds like the engine is trying to work harder and it will eventually downshift (allowing acceleration again), but it will bog and hesitate once it upshifts again. It isn't until I press the gas pedal all the way to the floor and I allow the car to downshift and zoom ahead a bit that the problem will subside (at least for the time being). It doesn't seem to be a problem at highway speeds (40 or so +) but more so around town stop and go.

Here is what has been replaced on it:
-Fuel tank
-Both half shafts
-Throttle position sensor
-Valve cover gasket

Plugs don't look too bad. Wires and dist (at least the cap) looks fairly new. I just think it's odd since the problem won't go away until I open the throttle all the way (95% won't do it). Any ideas?