I would look at the switch first. If you have a mechanical gauge you can check the switch, if not no more than a switch cost, just replace it. Oil pumps usually don't just fail.

 

It seems like a no-brainer to change the oil pressure sender before changing the pump.

Is that a 4.7? I think that the sender may be down in the vicinity of the oil filter. At least it was on the earlier 4.7s.

 

It seems like a no-brainer to change the oil pressure sender before changing the pump. Is that a 4.7? I think that the sender may be down in the vicinity of the oil filter. At least it was on the earlier 4.7s.

3.7. Sender behind oil filter. 266k miles, oil change coming up. Will check/change then. May use higher viscosity oil due to age and mileage. Any recommendations?

 

It probably calls for 5-30?
I think that if it was me I'd stick to that.
I use Mobil 1 full synthetic, but if you've got 266k and it is still running good, whatever you have been doing is working, so I'd say probably keep on doing it.
(I have read very good things about Amsoil.)

 

Update to pressure switch problem. Finally able to remove switch. The switch connector was filled with oil. That was the source of oil leak and caused the low oil pressure light.

 

Thanks for the update. Some day down the road it may help someone out with the same issue.