904 trans issues in need of help

[Kris wolf]

Have a 904 trans that will pull in reverse first an second no noise not slipping but sounds like you dropped a metal garbage can down the stairs filled with rocks in drive . Replaced the slip yoke on driveshaft as a cheap maybe fix ujoint was bad anyway. the fluid is fresh an clean with new filter an full. Anyone have a idea short of ripping it out to rebuild it.i thought could be flex plate but it should make noise in all gears I would think . An yes I know I need 2 clean the shop