flat spot in low end acceleration

On my 1990 GS I have this spot usually between 1st and 2nd and 2nd and 3rd (automatic) that flattens out and loses power briefly. I happens in normal driving conditions, if I floor it, it seems to pass over the spots. I can't get a smog test because they get a message of "bogs under load" before any testing begins. I've taken it to a couple of mechanics and they can't figure it out. There's no check engine lights, it's not the plugs and wires, not a throttle body sensor and it's tuned up fine. Does anyone have any idea what this might be or what I could check to figure it out? Thanks.

So it actually just skips for a second and has no power? I would think it either has to do with the fuel or the tranny.

:confused: spark plugs...I don't know, have you changed them recently? are they due for a chane? doesn't really make sense becasue its at specific points but you never know.
I don't think it is the fuel, more like a fuel filter which is dirty or so and whenever the switch frin 1~2 and 2~3 (quicker combustion) occurs more fuel comes and can't passed it right at that instant...

I just changed the plugs and wires with NKG parts and it really is no better. I'm not sure it's the tranny, because it shifts smoothly for a few minutes first thing in the morning. There is a rough idle when I'm in gear (especially reverse) but the fact that it won't pass the smog because of bogging makes me think the problem is elsewhere. I'll check the filter but I think it's been replaced recently.