1997 Ford Explorer performance

I recently purchased this 97 ford explorer, and had the transmission rebuilt. I changed the plugs, the fuel filter, the battery, the egr control valve, 1 pre catalyst oxygen sensor.( Because the check engine specified that one). Cleaned the throttle, changed the oil, and put a bottle of fuel injector cleaner in. I recently took a trip through west virginia. And it's a lot of highway up and down pretty steep hillside. When i'd be flat or coming down a hill. No problems, decent acceleration, and decent power. Enough anyway. Uphill, is a totally different story. If I act like an 18 wheeler and get up enough speed and don't have to let off the accelerator or brake as i'm going up, no problems. But on my way up, if I have to let up on the accelerator even a little bit, or god forbid press the brake pedal, maybe if some one is going too slow, or cuts in front of me, and then try and reaccelerate, no go. I basically have to floor it, and even then it will just kind of feel like it's hanging in limbo. No acceleration, no power. The rpms will kind of just sit still almost, and then sometimes they will rev really high like 3.5 rpms. And it will kind of punch or kick. And then I can accelerate. Then I can let the pedal off the floor at least. But that doesn't happen all the time. It seems it depends on how much I had to slow down. If I have to slow down too much. It seems the chances are less that this will even happen. Like 3 or 4 times on this trip I floored it with no response at all. No rpms reving up. And no punch into power. Can you help me?