GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hi there, I am Cam. On your van, when does it vibrate? What speeds? what conditions? What gears? Is the vibration fast like when driving over rumble strips or what?
Does changing lanes seem to change it?IF not then with the difference in speeds I would be thinking there is a problem in the drive shaft or rear diff. First lift the van and support the axle, put the van in gear and watch the drive shaft spin. It should have less than 1/16" wobble. If you find issues, have it repaired by a driveline shop. If not, then the rear diff.
Take the cover off and inspect the gear set, oil and magnet for signs of debris, metal and repair as needed.
If you find nothing in the diff either then your issue is in the transmission and it will need to be rebuilt.
what speeds does the vibration occur?