I've got a '97 SLS that was having trouble shifting the last time I drove it. I did a WOT to get to 80mph on the interstate, but then the rpms stayed at 3000+ when I started cruising like the overdrive never kicked in or it never shifted to 4th gear. The car continued to shutter and was having problems finding the proper gear. The SES light came on from code p1520 transmission range switch circuit. There are a lot of posts on here from people tripping that code, but there is very little about how to fix it or what the problem is. A couple people went to the dealership...is that my only option? Should I go to the dealership or a tranny shop? Can someone post about how/what they did to fix this issue?