Shuddering/Lugging of engine
 

I recently purchased a used 2005 Volvo T5 XC90 w/83,000 miles. When driving on smooth paved roads I notice a slight shuddering/lugging of the engine, especially when on a incline @ speeds around 40-60mph. It is also noticeable @ highway speeds just not as much. It is more noticeable on smooth roads, typically you can't notice it very well on rough or bumpy roads.

I've taken the vehicle to the Volvo dealer and the scans on the vehicle came back with nothing and the check engine light does not come on so it's not a easy problem to pinpoint. The service manager didn't beleive they could address the problem @ this time. Since then I've called a couple mechanics and the first mentioned possible CV joint issue, the second mechanic mentioned using premium gasoline or could be a the torque converter just not bad enough to send a bad signal to the computer. I should note the shudder is in the body of the vehicle not in the steer wheel. Tires are fairly new. Any ideas would be greatly appreicated. Thanks, John