shifting problem along with tachometer and speedometer not working

The ignition module is under the hood inside the distributor. It could cause the tachometer to stop working but would not effect the speedometer. For the speedometer and shifting issues I would look at the data from the vehicle speed sensor. The transmission control module bases shifting times and quality based on the calculated engine load shifter position and some other items. The VSS is one of them and it is the primary signal to the speedometer as well. It is mounted on the transmission tail shaft extension and held in with one bolt and has a single electrical connector.

For the tachometer. I would check that the white wire that attaches to the ignition coil is good and connected. It is the wire that sends the rpm signal to the cluster. The ignition module uses the pick-up coil in the distributor and other signals to determine ignition timing and control that system. The normal failure mode is not that the tachometer stops working, instead the engine will just crank over and not run.
To test is properly requires an old style tachometer that you connect to the tachometer test point (short piece of white wire taped in the harness not far from the ignition coil) If the tachometer works there the cluster may be the problem. If it does not then you hook directly to the coil and test there.