lately my transmission wont shift into top gear on freeway. instead of shifting down under 2000 rpm it stays up at 2700 rpm. transmission does fine otherwise, this only happens half the time. the other half it runs fine. i so have a knock sensor reading on my checkengine light..everyone saying its going into limp mode because of knock sensor. i was quoted 1100$ to fix the sensor. so my question is there any way to bi pass the sensor? my van has 220000 miles runs great other than this and just want another year with the van without dropping money into it..than ill get a newer one. also will it hurt my engine to drive in lower gear on freeway?