91 ES250 Loud Throttle Noise

The engine was running very smooth until we took it in for a tune up. Mechanic suggested we change one of the engine mount and performed the task. Now the car runs quite noisily, especially when gear is shifted, as if it's throttling very high. Call back the mechanic and he claimed it's the way the engine should reve. He also claimed he did not adjust anything on the engine. Took it to a Lexus dealer and they cleaned the gunk out as a minor service but the problem still persists. Dealer suggested to change the remaining 3 mounts! My question is could changing one mount cause the problem? I now feel like I'm driving a truck and not a smooth well-tuned Lexus. Please advise.