Oil pressure concerns

As above, pressures sound good hot with 10W30.

Synthetic is not going to particularly clean out the engine. High detergent oils will. So a Rotella-like oil, with high detergency, would clean it up. But your pressures don't sound like you pickup is blocked; you would expect to see low/erratic pressures at cruise if that was the case.

As for the 2-3 second delay in pressure build, the anti-drainback valve in the correct oil filter should help that for shorter stops, but 2-3 seconds when cold is not abnormal.