Look for a "Little Old Lady" car at a junkyard with a Q-jet on it. More times than not, those are good carbs. Also, there is a mixture controll module on the later q-jets. If your TPS or O2 sensor is out of whack, this will cause the conditions you describe. My personal guess is leaning towards the TPS as it is dominant towards higher RPMs. Youll find it towards the front, left side of the carb. If theres not a connector there, ignore everything i just said:P