93 vic trans problem TR/MLP?

[3rdday]

My 93 crown vic has an intermittant trans problem. When cruising at a steady speed it sometimes decides to upshift to nuetral or downshift and then shift up again. It acts like it can't make up it's mind what gear it should be in. If I stop the car and manually shift to low and then manually upshift as I accelerate the problem does not reoccur. The Consumer Reports for used cars says that this problem is caused by a bad TR/MLP sensor located on the side of the trans. Is this sensor a big deal to replace?