Successfully took the truck on a 475 mile road trip recently without issue, except for developing a driveline vibration at high speeds. Here are the symptoms:

- No vibrations until 60mph
- Vibration felt from 60mph-70mph
- Vibration peaks at 65mph then disappears by 70mph
- Vibration seems to be magnified if I take my foot off the gas pedal and let it coast until it gets below 60mph then disappears.

I'm thinking either engine motor mounts or my rear driveshaft. Thoughts?