The oil pressure wont change if its a little low. The pressure is from the pump that is submerged. it doesnt care what the oil level is, as long as the pickup is under oil. If it comes out of oil, pressure drops to zero, it cavitates, aerates, and causes bigger issues than low oil. The thicker oil will result in higher pressures as its more difficult to push it through the orifices in the engine. Specifically the Rhodes style high bleed hydraulic lifters. They compress at low rpms absorbing some of the lift from the cam, improving idle, throttle response, vacuum, and emissions. At higher rpm they pump up hard and provide full cam lift to the valves. The thickness of the oil effects at what rpm these lifters pump up. I speculate the thicker oil lowers the rpm that the lifters produce full lift.
The importance of the proper oil level is so that the crank has enough oil to slap, and drag up and splash the bottom of the pistons and cylinder walls to keep it lubricated. Because the crank is round, the importance of the level of oil goes up exponentially. The lower the level, a drastic decrease in the available oil to splash on the cylinders. Additionally, when the oil level is too high, it causes parasitic drag, and the extra oil it splashes sometimes makes it difficult for the rings to swipe away. This can cause oil burn and smoking.
The cable style dip stick with the barrel end and the pentastar emblems on it , i think in the 04/05 were notoriously hard to read. Especially with fresh oil in it. A trick on those is to spin the dipstick before you remove it so it evenly coats both sides. Also you can get some 80 grit sandpaper and scuff up the barrel so it clings more oil. If you have the flat blade style dipstick like i do, it should read evenly on both sides of the stick. If its not its likely you have low oil level, and you are wiping it down the dipstick tube.
I would get 2-3 quarts of oil, next time you do your oil change, add them to it, before you drain and see if the stick reads proper when you add oil to it. That way if you put too much you can drain it anyway.
