I'm sure my car has done this since I purchased it, but I really noticed it yesterday. When I floor it in first and take it to around 5-7.5 grand and either let of the gas by kicking the clutch, or just shift into second, my shifter shakes real bad. As well as my car it seems. I'm assuming that my engine mounts are fautly, or possibly my transmission mount. My exhaust (3.5 downpipe, cat, 3.74 catback) isn't on the middle hanger so that could be shaking. But I doubt that has enough power to hit my tranmission and in turn move my shifter. I'm going to bolt my exhaust to the hanger soon. I hate half assed shit.