Diagnostic trouble codes P0172 and P0175 on your 1996 Ford F-150 indicate the fuel adaptive system is maxed out at the lean correction limit -- P0172 in bank No. 1 and P0175 in bank No. 2. A too-rich condition is detected in the air/fuel mixture and the PCM can't compensate.
If the codes appeared after you changed the air filter or the thermostat, double-check what you did. If you put in the wrong air filter -- double-check the part number -- or if you didn't latch the air filter canister, you could have popped the codes yourself. Likewise, if you removed the thermostat and left it out, or you replaced the thermostat with one that has a lower temperature rating than the recommended 192 degrees F, shame on you. Check the engine oil; make sure it hasn't been overfilled and double-check that the dipstick is seated.
If the truck bogs down during wide-open throttle, you may have a restricted exhaust. A bad PCV or EGR valve might be the culprit, as could induction system leaks -- vacuum leaks or air leaks after the mass air flow sensor. Also check for obstructions in the air intake. Cam timing, bad spark plugs or coils, or incorrect fuel pressure at the fuel rail can also pop those codes. To diagnose this correctly beyond the obvious, you'll need a scan tool with Live Data capability. Don't assume the fuel pump, fuel pressure regulator, injectors or oxygen sensors are bad. It might just be a bad MAF or coolant temperature sensor.
