The whole "bypass when half full" sounds kinda fishy. I have never seen a pump that works like that. Reason #1 is that it would need to have same means of closing off once you went past 1/2 a tank or you'd be sucking air. Reason #2...why go through that extra design work when having just one intake at the bottom would work better anyhow and cost less to manufacture.
I *think* that the fuel filter/pump is an integrated unit but I haven't had a need to take mine out yet so I won't call Bravo Sierra just yet on the 1/2 full speculation but like I said it sounds fishy.
Also, I would bet that these are not directly built by MC themselves and one can likely get them cheaper from somewhere else. I know the fuel sender guage was a bit cheaper on the open market.
I'll pull the floor when I go out on thurs and see if I can find any identifying model numbers on it.
Tough one Joe, off hand I'd say check the fuel pressure with a guage and if that's ok then I'm thinking dirty injector(s) or bad connection to the injector(s). You can check the injector connections with a multimeter, now sure how to check their dirtyness other than cleaning them. Maybe Throttle Position Sensor check also? This is assuming that the spark plugs, wires, and distributor (if you have a distributor), are all ok.