Stanleys

Our 94 Pathfinder idles beautifully. When we give it gas, it hesitates and sputters terribly. The previous owner said it sat for about 8 years. We had to replace the fuel pump and fuel filter and flush the gas tank due to rust and junk. The speedometer has jumped around but it ran. Now, it will not pick up speed. Starts and idles. We coded and got a 13, 14 and 51. One injector we replaced and have not reset codes to see if that injector fixed code 51. The other two codes are for the vehicle speed sensor and the engine temperature sensor. Can these be tested and if so, can you direct us on how? Thanks