High RPMs low MPH

I have an automatic 98 Saturn SL1. A few months ago my car started squeaking so I took it to a mechanic and he said that it's probably the speedometer cable and it just needs some lubricant. I let it go and dealt with the annoyance, after a while it went away on it's own. Then a couple weeks later I was driving and the SES light came on the RPMs began to shoot up but I only got up to 20mph. I turned the car off for a while and it drove fine, but the problem keeps coming back sparatically. Does this have to do with a faulty speedometer or is this some other problem? I took the car to two different places and all they found was a bad caty (which I got replaced), and the other place got codes po731-734. I really want this problem fixed, the closest Saturn dealer is about 1 1/2 hours away so I want to make sure it's not somethign basic that could be repaired close to home. Please help.