First, are you using the same weight you were using before?
Second, oil pressure is a good indicator of worn bearings, as the bearings wear the oil pressure decreases because there is less resistance to flow. But the comparison would be made with the same oil and weight as years and miles go by.
The decreased oil pressure in and of itself by changing oil would not be anything to be worried about as long as the pressure didn't go alarmingly low. The over the road Cummins engines have their oil pressure regulated to about fifteen psi maximum. This is done to eliminate energy waste driving the oil pump. As long as there is enough pressure to cause oil flow, there is no ill effect.
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in