Car loses power after it shifts?

My 1991 Honda Accord (automatic transmission) will occasionally do this thing where after it shifts the eltric components go out and come back on all in a matter of a second. It's not long and the engine doesn't die and it's almost like flickering a light switch quick, noticeable but not if you weren't paying attention. I just replaced the alternator about a year ago and all the belts are good. I've also noticed that the car will idle at very low levels when I come to a stop. The headlights even dim a little. But once I accelerate its all back to normal. Any ideas as to what may be happening? Old transmission? Maybe just needs new transmission fluid?

Hi so what do you really expect from a 25 years old car might be the issue here.