Transmission worries th350?
I'm not quite sure what your asking. The 350 does have 13 bolts for the pan.
The direct clutchs apply in 3rd,does it also slip in reverse[directs apply in rev as well].
I want to help you,but slipping in 3rd is not usually something simple.
It sounds like trans has given up the ghost.
Are you capable of working on this,if so I will be glad to help you thru this site.