vibration in 2001 GMC Serria
 

I am experiencing some sort of vibration during accelleration on my 2001 4x4 serria. It is mostly noticeable from 50 - 65 mph. I have also noticed it at lower speeds. I have had the tires rotated and haven't had a chance to get out on the interstate to see if that has helped. If not, what else might it be?

First time poster

Mike