Major hesitation when trying to accelerate

I'm getting a major hesitation when trying to accelerate. At first it was only at 60 mph. And when I tried to overtake on the highway. I have replace the plugs and coil packs. Replace fuel filter. Had a conditioning done to engine. Cleaned an checked the mass air sensor. New air filter. New fuel module sensor. And now the truck is hesitating at all speeds. Much worse if the fuel is below 1/4 of a tank. I took out the coils and plugs again to check for burning etc, but all looks good. I'm at a complete loss. The only thing that I can think of is the fuel pump. It seems that after the hesitation it delivers fuel okay. There has been faint smell of fuel when stopped at a light as of late. There are no codes and no check engine light. It has been scanned. Any idea? I'm at a loss. Literally.