2003 F350 7.3 diesel eng light comes on and stays on after start-up. As of to day have replaced exhaust back pressure sensor, injector driver mod,ecm and cleaned the fuel filters in the tank, I do regular oil changes but have changed oil and filters and fuel filter. What do you think is happening?

Attach a code reader or scan tool to the data link connector and find out what code was thrown.

I agree.. until you know what codes the computer are showing... you could theoretically replace all the wrong parts before you get lucky and find the right one by chance.

I too agree with smoothy that you need to have perfect knowledge about the problem and the solution and you should not try different things without any complete knowledge, which adds extra effort and loss of money as well. You must contact someone good at repairing car.