car moves slow in gear

Sounds like your friction is not being applied properly, which can be caused by control/apply electrical/mechanical components such as computer, solenoid valve, valve body, pump or can also be caused by worn out friction as well such as clutches. Many control problems often can be corrected quicker and for less cost, whereas pump, friction type problem would require transmission removal and overhaul or replacement. Need to start by having vehicle towed to a quality repair facility for diagnosis.