Help 99 Silv

While sitting at a stop sign or light my truck revs down, lights dim, revs up lights come back to normal, revs down, lights dim, revs up....etc so on and so forth until I take off. Any reasons? No other problems except after it sits over night it idles terribley on first crank, and has a small split second hesitation before accelerating. After that, it does the rev thing sometimes and sometimes it doesn't. Runs great all day after that. I have checked fuel pressure regulator and it's fine, just had new fuel filter, plugs etc...done. Fuel pump doesn'r whine...what could it be?

Anyone?

My old 88' tarus did the same exact thing, except when it reved down it would stall if i dident give it some gas. I dont know why it did it, that car was just a pice of shit and i was glad to get rid of it.

alternator???

Idle Air Control Valve?? Not sure if the 99's have one or not???