95 dodge Ram Hesistation

I have a 95 Dodge Ram 5.9 L 360 that hesitates when slowing down, backing up or taking off. It doesn't always do it, but the rpm's dip low enough that it dies sometimes. Also when slowing down the rpm's dip low enough that it losses enough pressure that it makes my breaks feel like they are going out. It has done this since I have owned it. I have taken it in before to a couple of different shops and they couldn't figure out what it was. I have replaced O2 sensors, the idle speed motor, plugs & wires, and air filter. To me it seems like an air or vaccum problem, but honestly I have no idea, it is just really annoying. Let me know if anyone knows the real solution to the problem.