My oil pressure gauge jumps like crazy when at idle after the truck warms up. The idle is at about 600-650 rpms. When I hith the gas and raise the rpms to about 900-1000 rpms it stops jumping. I changed the iol pressure switch and it didn't do any good. I just changed the oil and used Amsoil 5w20 full synthetic high millage and a wix filter. I checked the oil level and it's where it is supposed to be. The manufacturer recomends 5w20 for the '02 ranger 3.0 but I have heard that with 189000 miles it might be a good idea to switch to a 30 weight oil. I don't have any knocks, tics, pings, or whining but the oil pressure registers prety low. See atachment for clerification.

Any ideas or advice would be greatly appreciated.