transmission not shifting on 1992 Volvo 940

what happens if i continue to drive the car with the transmission not shifting at 60 mph?

2 answers 2 comments
what gear is it in, and what are the rpm's when you are going 60?
it is drive and the rpm's are 3 to 3.5
If it isn't the kick down cable, could a bad solenoid be the problem? how much would it cost to replace a solenoid? what other potential problems could it be?
It maybe you the over drive relay that is the culprit. They run about $30-50.