It may be that you were struck by the gods of coincidence, in that the oil pressure reading started acting up right after the gasket change.

Can't hurt to change the oil pump.

Keep in mind two things: (1) Oil pressure generally rises with rpm -- the more you rev the engine, the more pressure you'll see. (2) When the engine is cold and the oil is thick, you will often see a higher oil pressure than you will after it warms up and the oil thins out a little.

I have known several engines to have oil pressure drop to as low as 10 psi when idling a warm engine, yet everything works ok. If your lifters are collapsing, then it's time to worry.

Before the gasket change, what was the oil pressure on an idling warm engine?