My bro is very close to getting his 87 GN back on the road, but before he parked it for the engine rebuild the tranny would severely slip on the 1st-2nd wot upshift. He has the money to rebuild it what would be a good thing to do, buy a rebuild kit and take it somewhere? Or just take it to a reputable transmission shop and let them do it? He wants it to be able to handle 450hp to the wheels and wants nice firm shifts. Does anyone sell a good tranny overhaul kit?