Glad you unblocked the relief valve; that can become quite problematic.

Can't say I've ever seen a dowel pin fall out before, but given the shape it appears to be in, I'm willing to bet it got in the way at some point after falling out.

Still sounds like the clutch is dragging though. Do your synchros a favour: avoid any and all driving until this problem is resolved. I'm quite confident it is a clutch issue; the tranny CAN be spared, if you stop driving on it!