Oil

Have you had an actual pressure reading or just the gauge? Have you tried a heavier weight oil than is called for like 20/50? Or use an oil stabilizer like LUCAS brand? Do you mean pressure reads low while actual driving? Or just an overall lower range of pressure? And hot oil will register lower than cold oil anyway. The hotter it gets, the lower the reading.

I DO NOT recommend using 20W50 in that vehicle. You can't really use oil that heavy in anything built after the early 90s. The engines were built differently with a lot smaller oil clearances, designed to use thinner oil for better fuel mileage. If you use oil that heavy you will get "dry starts" which will lead to heavy engine wear. If you have an oil pressure issue, repair it mechanically. If you have an oil consumption problem, then maybe consider the additive but not the heavier oil.

If your oil level I slow then add, but have a mechanical gauge installed and read it that way. Yours has electrical readings and either the sender or the gauge cold be screwing up. If you are losing oil and not seeing any leakage then it would be burning it maybe via the head gasket. It could also be valve seals/guide wear. I kind of doubt that however.

I use 20/50 in hot weather. 5/30-10/30 in cold. If oil is low, you could add just a quart of 20/50 to raise viscosity. As far as dry starts, I use LUCAS stabilizer to help with that, as a side bonus it also reduces small leaks/seepage.

NO, do not use 20W50. It will do engine damage in that vehicle.