Your speedo, transmission and stalling problems are not related to each other.
Speedo: most probably a loose gear in the speedo itself or a defective speedo cable/Grear.
Stalling: Could be many and several things. Fuel related: Filter, pump, fuel distributor. Electrical related: Spark plugs, distributor cap, rotor, spark plug wires. Vacuum leaks, idle valve,
Transmission: A simple oil/filter change could possibly solve your problem or there are some mechanical problems with the transmission.
I think you need a good professional diagnostic before throwing $$$$ at replacing parts to solve several unidentified problems