slip yoke, joint ? bad?

I have volvo vnl 670 it is 2011. I have some vibration and i feel it around 55-60 and they around 65 is going away but not all the way i still can feel it under my seat and the cab and in the steer, but im sure its not the front end. I check rear u joints not movement. The only movement i can feel is that u-joint behind the transmission nut, but it’s a small movement. You have to watched and move the yoke up and down and u can notice its bouncing but like i said so small movement. It might be that what is causing vibration since the mechanic said they check them and they are fine. Sometimes if its not big movement they will be like its fine which it happens to me and i don’t beleive them sometimes. Thanks for any opinion.

 

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