I have an 01 SS completely stock with only 76,000 miles. Gears 1-4 work perfectly but when I go into 5th sometimes it grinds and sometimes it pops out into neutral. Sometimes it locks when in 5th and I have trouble going into any other gear. It locks while driving and when it's off. When it's off it seems I can't go into 6th. I would appreciate any advice anyone can give me. Do you recommend me to rebuild the tranny or is it something more simple that I can check and replace?