340lph is a LOT of pump for a ~400HP motor. More isn't necessarily better with fuel pumps. Anything that's not being used is getting recirculated back to the tank, so with a larger pump you're just recirculating a lot more fuel, causing heat buildup and aeration. I have a 255lph Walbro on my gen 2 coyote (435HP) and that's plenty of pump for an engine of that HP.