Okay everybody I am new to this page and am seeking some help considering I can't find it anywhere else . I have General mechanic knowledge and just picked up a 2002 wrx sedan 2.0 with a blown trans . I purchased a new trans out of an 03 wrx and installed it last night . On the test drive I drive around for a bit and had no issus but never hit over 40mph in town . Now I hopped on the freeway and as soon as I hit right around 60 mph the whole car started vibrating violently until I conpletly stopped . Car still idled fine . As soon as I started driving again the vibration was gone and drive 100 percent normal until I hit about 60+ mph once again . Everything is right and wheels are balanced any suggestions ? Could the rear diff be the wrong gears ? The guy I bought it from said he replaced the diff a week before the trans blew and said he was cruising on the freeway when it happend ? I was thinking that or the driveline what do u guys think ?!!