If this is primarily a street car, IMO you have a bit too much carb for the engine and I've personally always preferred a vacuum secondary on a street car with an automatic trans. I think you'd be a lot happier with a 600 or 650 vacuum secondary carb. The oil pressure loss could also be carb related, if it's running that fat you might have pumped a bunch of that excess fuel into the crankcase where it's mixing with your oil!!!! I'd check to see if the oil smells like it has gas in it.

The 750 DP is a great carb, but probably not ideal for your application!