Recently bought this 93 ex cab 4X4. 150K miles. Engine replaced with used one b4 I bought it. Previous owner said speedo never worked, even b4 engine r&r. Where to start? Everything else works except does not blow heat. Luke warm. Changed heater core, thermostat, radiator, hoses, etc... Hoses into core are hot. Please help. I want to put truck 4 sale as soon as speedo is fixed. Thanx!!