The oil pressure guage on my 2006 nissan frontier is reading very high after recently changing the oil, however, the correct amount of oil was added during the change. Furthermore the oil dipstick indicates the correct oil level was obtained. I've changed the oil in this vehicle many times in the past, and this has never happened. The gauge generally sits right in the middle under normal operating conditions.

Here are you oil pressure switches,there are 2 types,one for light on dash and one for a guage,it is screwed into engine by oil filter,may have to remove filter to get to switch,may need a stubby wrench to remove,tight area.Take to Autozone and match up to be sure.

First thing is find out if the oi pressure is really high. Remove the oil pressure sending unit and hook up a oil pressure test gauge kit, if the pressure is within normal then replace the sending unit first. (requires a special socket)

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some say, it's good to have high oil pressure. but it is abnormal to the system. does it means there is restrictons from oil gallery that makes the oil pressure go high. any kind of motor or engine needs change oil. you had manaul recommending,when you change oil and what kind of motor oil you're going to use. change your oil filter too.

Not sure about the oil pressure problem. May be the gauge or sending unit. Does the engine start ticking or knocking when pressure goes low?If not you probably still have good pressure.
The loss of power may be a stopped up catalitic convertor. I've had one Frontier that this has happened to.

It could be a bad gauge or a check valve could be stuck or blocked causing your oil pressure to be too high. Have your oil pressure checked at a shop.

YOU MIGHT HAVE THE WRONG WIEGHT OF OIL

This is caused by a worn oil pressure sending unit. Have that replaced and you should be set. In rare cases the gauge fails, but this is extremely rare.

Have you checked low or high side pressure at idle?

Please understand, all I can offer you are suggestions, since I don't have access to hands on testing. You might first change oil and filter.
If going by the oil pressure guage, low oil pressure can mean worn crankshaft bearings, as the clearance between bearings and crankshaft is what determines oil pressure.
Of course a worn oil pump can cause the same problem.
You might want to connect an external oil pressure guage to the engine to verify the pressure reading.

The rough running at this point would be hard to pin poit.
Because I do not know the extent of the rust, I can suggest that you consider having it undercoated.

Again, I can only make suggestion because you need an absoluate diagnosis.
jetski