Yikes, is there no happy medium between the two?

With 135,000 on the clock and this thing moving fuel, I’m sure you will need all of the gaskets and o-rings also, but at nearly $600 I might go with the less expensive pump and see if ECS also sold just the gasket and o-rings - may... save you a few bucks.

That said, I would check the fuel pressure at the rail and also maybe consider checking the fuel pressure regulator. Wondering if it’s a fuel delivery issue coming from the pump or the FPR not holding pressure at the rail... - that said, I have the 4.4 so I’m not 100% sure on how yours is setup.