Looks like you are having the same problems with your car that I had with mine. When my knock sensors went out, the check engine light came on and the car would not go into overdrive. Needless to say if you are driving the car a lot on the highway at 70 MPH, your RPMs are going to be pretty high if the transmission is not shifting into overdrive. Yes, driving the car for extended periods at high RPMs could cause engine damage. I had my transmission rebuild a year before the knock sensor went out. So when the car would not go into overdrive I thought I had transmission problems again. I took it back to the transmission shop and they diagnosed the bad sensors were causing the transmission not to shift. I had AAMCO replace the sensors for me, which fixed the Check Engine and Shifting problems.
