I just put a walboro 255 in the same truck, the stock pump lost pressure at 4500rpm causing a 17:1 AFR. The new pump solved that problem. It took about 2hrs to install from start to finish, I used a cherry picker to lift the bed and pulled the sender out the top. I had to solder two wires to connect the pump and use a piece of 5/16 fuel hose. Pretty easy install, a lot of the time was spent rigging the bed for lift off.

 

I had an issue like that once. It was the injector clips. Follow the two wires that run into the injector clip, the 2 metal connections inside the plastic clip had worked themselves loose. (spread apart) I squeezed them back together so they would have a tight fit on injector studs and snapped it back on the injector and it was fine. I was throwing misfire codes as well. Of course it took me 3 days of troubleshooting to find that simple problem