Re: shift solenoiod C
It could be a bad solinoid or a bad connection on the wiring. I would check the trans plug first for corrosion and if I didn't see anything there I would drop the pan and pull the solinoid and check it with an ohm meter and test it on the battery voltage. If it clicks I would say it's good. and consider a valve body gasket/filter change.
22 and counting...