02 ford explorer won't accelerate past 3000 rpm?

As I was getting onto the highway, I tried accelerating to match the speed of the other cars and the explorer wouldn't go past 3000rpm or downshift. It was making an odd noise kind of like a grinding of gears maybe? The transmission slipped a couple times a few months ago but nothing since. Check engine light was already on for gas cap leak but double checked it and that was the only thing wrong. The engine went back to normal on my way home which is when I checked the engine light. I apologize for the long read but need to know what it is before it breaks completely. Btw it has 164k miles