Post Ignition Hick up

I have a 96 Dodge Stratus 4 cylinder 2 door car. It has about 100,000 miles on it. It was purchased in the Chicago area, but we now reside in central Texas.

At about 75,000 we noticed that it would hesitate when it hit 60 miles an hour with an rpm of 3,200. At that time we took it to dodge and they could not find a problem. At 80,000 miles we made some mistakes and had to replace the engine. We replaced it with an engine with about 70,000 on it. The hesitation problem continued. We were told at that point that it must be the transmission. Recently we had to replace the transmission with a rebuilt transmission. The problem with hesitation at 60 mph continued. We were then told that it must be the ignition coil. So we replaced the ignition coil, but it still hesitates at 60. We were then told that it was the catalytic Converter. So we replaced the catalytic Converter, and it still does it.

We have endured this now for a couple of years, though a lot of new parts, and still have not found the answer. Any suggestions?

Thank you.