96 chevy truck idle vibration

Hi, I have a 96 chevy truck with the 5.7L vortec engine. When idling in drive i have a vibration. the best way to describe would be if i had a glass of water in the truck it would ripple and shake. Also, you can feel the shaking in the seats and steering wheel.

Now when I accelerate it goes away and is very smooth, also when idling in neutral the vibration goes away. I changed the oil and spark plugs and it helped some but is still there. Maybe it could be engine or tranny mounts, but I’m not sure. Any help is greatly appreciated

Try cleaning the throttle bore. (air intake)