Hi Texas

Not an easy one to diagnose. Here is what I am guessing.

Your initial problem was that the heat was staying on, but you did not notice it. This caused your hi limit therm to blow, which of course you did notice. When you replaced it you now reverted to your original problem. (if you were to leave the dryer alone it would probably blow the high limit again)

You could replace the cycling thermostat on speculation, it is not expensive and see if that cures anything. If not, we will have to move on to more expensive parts like the timer.

Good luck, let us know what you do.