I am not clear what you are referring to when you say "shifter swivel lever".
I do know that if everything is in good shape and it still jumps out of third gear than it is an alignment issue.
To remedy this you need to shim between the bellhousing and trans case. This puts the input and main shafts in alignment so the synchronizer drum is not walked off the third gear teeth. It is described in some of the shop manuals.
