Hello and welcome to JustAnswer!
Have you checked the oil level?
How many miles are on your truck?
How often do you change the oil?
ARe there any abnormal noises when the oil pressure drops?
Did this only start after the oil change?
What brand of filter did you use?
Have you always ran it a quart low on oil?
So it was doing this both before and after you changed the oil then?
Your truck holds 7 quarts of oil. It would be a good idea to put the extra quart in and see what happens if this only started after the oil was changed.
Was there an oil change sticker in the window? If so, was it over on mileage (how far?)?
Does the pressure only drop when the engine is hot?