1996 Explorer Hard Start & Rough Idle

After installing a new fuel pump, paying for a complete tune up and even buying a new battery, my 1996 Ford Explorer XLT with Six Cylinder engine with 135,000 miles is still hard to start and idles at a low RPM. It runs okay once you put the accelerator to the floor (briefly), start the motor and keep her idling at between 1,000 and 2,000 RPM until the cold weather choke engages (which is usually between half a minute and five minutes). But then, after it cools off when parked for a few hours, I have to go through this whole process again. And when I’m on the road, there’s that constant bee hive buzzing sound coming from the rear that makes you think she needs another fuel pump. But it’s brand new! What did my mechanic miss?