Vibration between 30 - 40 MPH

I have a 2017 Freightliner Cascadia that had developed a serious vibration starting softly at 30 MPH peaking at 35 MPH and then stopping around 40 MPH. I have checked tires and got them balanced. I am needing help figuring out what the next best thing to look at will be. Thank you.

 

Check driveline. U-joints etc. Do your engine rpms make a difference? Kinda slow speed for a vibration.

 

If it's a manual throw it in neutral when the vibration occurs and let it go to idle. Should help you isolate the issue a bit.
I just had a similar vibration at 45 to 50 and it was u-joints. Pretty common and fairly easy to confirm by crawling underneath and giving everything a good tug. Check the carrier bearing while you're there.

 

it is worse when accelerating and I’m not sure if vibration is the correct word. It more shakes violently.

 

Shakes like a bouncing or shakes like the steering wheel skakes/jerks back amd forth?

 

I've seen a rock between the drives cause a heck of a vibration but that's near impossible to overlook and not likely on a highway truck.

 

You sure you don't have a misfiring injector. Happened to me once and it shook the hood etc.

 

Yeah I popped a tire once with a rock in between.

 

It kind of feels like I’m sitting On one of those exercise machines that just shake you a lot when you stand on them. But worse.

 

I haven’t had the injectors checked yet. Never even crossed my mind that one could cause that. Thanks.