94 Caravan transmission question

Hello. First off I am sorry if I keep asking questions about this same van as I am sure you are all busy people. But my brother is very poor and he can not afford a new or different vehicle so I try to keep
him running with my limited mechanical skills and junkyard obtained parts. So...I have a 94 Caravan 3.0 engine automatic with a 3-speed transmission. The old transmission went up and we got a replacement from a wrecked van at the junkyard. It seems to work ok and goes forward and backwards and gets up to a steady 50 mph. However I think it could work smoother and go full highway speed if I could fix one nagging problem which seems to be of an adjustment type I hope. On the top of this transmission is a 2 piece lever which has one part connected to the shift cable and the other to a solid metal rod which connects to the throttle. They should operate independently but these seem stuck together in some way and will only turn together (When the gears are shifted) which is affecting performance. I don't want to just force them apart and break something. Any advice on what could be a cure or is this unit replaceable with the transmission in place? Thanks in advance.

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