im getting a vibration which i believe is coming from the trans on my 2010 dodge ram 1500. it happens when i a reach a certain speed. i can accelerate to 40 and idle at that speed or 60 and idle at that speed. not necessarily a specific speed when it happens. it is happening more frequently. any ideas what might be happening.

 

I was offered my current truck for a price that I couldn't pass up -- it was a situation of just being offered something for nothing and I wasn't even looking to buy a truck. It had been sitting for six months. When I first drove it home, it had a shudder that is exactly like you describe. Although not a professional, I'm a fair auto mechanic and I would have sworn that I had a transmission problem. It wasn't. It was simply in need of a tune up. Plugs, wires, cap and rotor.
The shuddering was happening generally when the truck shifted into the next gear and the RPMs were low under load. When I pout my foot into it, the 5.2 was fairly healthy. But under load at low RPMs, it shuddered. I've seen ignition system issues manifest in exactly the opposite way until then.