Shaking when letting off the gas pedal at highway speeds…Help!

Hey guys, looking for some help. My 08 speed3 has a problem when driving on the highway. If I take my foot off the gas while in gear it shakes the steering wheel and dashboard pretty hard and won’t stop until I take it out of gear or give it more gas. I have taken it to a specialist who reccomended changing the driveshafts which did nothing and he hasn’t visually been able to find anything or get the car to shake while he’s driving it. Any help is appreciated, thanks!