2013 Express 3500 - 160k miles.

Recently had my terrible quality mismatched tires (came like that) replaced with high-quality new tires and alignment. It’s a lot smoother and quieter now, drives like a totally different vehicle. However now that all that tire noise and ruckus has disappeared I am sensing a vibration in the driveline, but only under drive. If I accelerate I can feel a vibration in the driveline, once I take my foot off the gas it continues for about 1/2 a second then disappears. When I press the gas again it comes back. My first guess was universal joints and/or driveshaft balancing. Any thoughts before I throw parts at it?

 

+1
under load the ujoint angle will change. remove the driveshaft and check for a tight ujoint.

 

I would start with simple stuff first.
Why not rotate your new tires and see what happen ?
Even new a tire can be defective. I saw this many times.

 

I thought of this but the vibration is only happening under drive - meaning only when I’m pressing on the gas and the drivetrain is making power. The vibration disappears almost immediately after releasing the gas. It happens from a dead stop when accelerating slowly (not going fast enough for tire vibration) and also when accelerating under load. There is also a clunk when shifting from park to reverse or park to drive, which also makes me think it’s driveline related.

 

Thank you, this is my next step. I’ll update with the results.