2004 Blazer Transmission 3rd Gear Lock
 

My daughter is on a road trip to a concert in LA traveling on Interstate 5. 10 miles north of Gorman, the transmission dropped into 3rd gear and would not go over 35 MPH. She is stuck in a small town with one general mechanic shop. He's not big on transmissions. Trans fluid was changed a few days ago along with the filter. She said there was a "rattling" sound that started at the same time it dropped to 3rd. It sounds like metal on metal. Anybody have any ideas about what we're dealing with?