lately my cars oil pressure has been acting weird, usually it is around 40 psi when moving and stays pretty steady and goes up at WOT sitts just above 20 at idle, but lately if im driving on the highway say about 60-70mph in sixth my oil pressure is only about 30. it will drop from 40 in 5th at about 2300 to 30 in sixth at about 1800 and it never used to do this.
i only have 120,000 miles on the car. any ideas of why it would drop to 30 in sixth but not in any other gear.

 

could be the pump. At the back of the lifter valley there is a gear that goes down to the drive shaft of the oil pump. This shaft is tunred by the camshaft. So the RPM of the engine is the most important factor. If you are seeing fluctuation in pressure at the same RPM, you should be thinking about looking at the oil pump.

The easiest way to get the pump is to drop the cross member. This can be done by renting an engine hoist. Support the top of the engine as the car is on jackstands. there are 2 bolts holding the engine in place, remove them. Then take the tires off. Then unhook the shocks from the lower a-arms. remove the brake lines from the calipers. There are 3 bolts on each side holding the k-member in palce, remove them and drop it.

You can then drop the oil pan and get at the pump. I have a new pump that i ended up not using, i will let it go for 30.