TRUCK STUDDERS UNDER LOAD & BETWEN 40 &80

It's might be immobilized try the spare key or get it code read that should point u in the right direction

SOUND LIKE IDLE AIR CONTROL VALVE BAD MASS AIR FLOW SENSOR.CAUSE ENGINE STALL OUT.MAKE SURE SPARK PLUGS AND WIRES OKAY.REPLACE FUEL FILTER SEE IF IT HELPS.IF NO CHECK FUEL PUMP PRESSURE AND PUMP RELAY.CODE SCAN FOR OTHER PROBLEMS LIKE FAULTY EGR VALVE.

COULD BE CLOGGED FUEL INJECTORS OR LOW COMPRESSION IF EVERY THING ELSE CHECK OUT OKAY BEEN REPLACED.

Lean fuel trim bank one and bank two, the oxygen is reporting engine conditions, you may have a lean misfire caused by worn sparkplugs, low fuel pressure caused by pluged fuel filter or a failing fuel pump, you are equipt with a MAF(mass air flow) under reporting or taking in false aire from a vacuum leak,you also have a MAP (manifold air pressure sensor) that can under report, For a 2003 the likely canidate for bank 1 and 2 to be lean is a need for a tune up , new spark plugs, the second fuel filter or fuel pump, and mosre likely a MAF cleaning why because when this sensor get dirty it under report the incoming air and gives less fuel. I threw the MAP in the mix but I doubt this would be a problem it monitors the EGR and if there was false air it would detect it and set of a MAP code. and ran the engine rich.

well it is a missfire the timing may be the issue here

I recommend you test your fuel pressure to see if it fluctuates any.If it were to be any of the other sensors you would have a check engine light that would come on.The only system that doesn't have any sensors would be your fuel system unless it has a fuel pressure sensor and you would have a light for that also.I would take a look at your fuel pump and filter.Also have your injectors balance tested this will tell you if you have any bad injectors or pressure regulator.

P0171 is a lean fuel condition . The computer reflashed has nothing to do with it . Vacuum leak intake manifold probably . If both P0171 & P0174 were back could be fuel pump low flow or restricted fuel filter . or O2 sensor problem or mass airflow sensor. Suggest you take it to a qualified repair shop to have it diagnosed .
Ford 150 P0171 P0174 Trouble Codes vacuum leak water test

Diagnosing Faulty Mass Air Flow Sensor P0171 P0174 Lean Codes

P0401- Exhaust Gas Recirculation Flow Insufficient Dectected
Possible causes - Harness or connectors (EGR volume control valve circuit is open or shorted.)
- EGR volume control valve stuck closed
- EGR volume control solenoid valve
- Dead (Weak) battery
- EGR passage clogged
- Exhaust gas leaks Possible solution - Clean EGR Valve
- Repair EGR harness or connector
- Replaced EGR volume control solenoid valve
- Replaced EGR volume control valve
Code P0171- Fuel Injection System Too Lean Bank 1 Possible causes - Intake air leaks
- Front Heated oxygen sensor may be faulty
- Injectors may be faulty
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Mass air flow sensor may be faulty
- Incorrect PCV hose connection Possible solution Dirty air filter of faulty air flow sensor are common causes of the problem P0174- Fuel Injection System Too Lean Bank 2 Possible causes - Intake air leaks
- Front Heated oxygen sensor may be faulty
- Injectors may be faulty
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Mass air flow sensor may be faulty
- Incorrect PCV hose connection Possible solution Dirty air filter of faulty air flow sensor are common causes of the problem.

Bad fuel, bad air filter,PVC valve, EGR valve

By a ford