Raising oil pressure by running a heavier than specified viscosity is like eating donuts & hamburgers to raise an abnormally low blood pressure.
70 psi at 2800 rpms is much higher than is good & that is strictly from running an oil that is simply much harder to pump... artificially raising the oil pressure. In other words, an abnormally high oil pressure is no better than high blood pressure is... the goal should be simply to have good circulation. A good rule of thumb for acceptable oil pressure is roughly 10 psi per thousand rpms. Have a mechanic check it out, maybe your oil pump simply needs to be replaced to increase your low rpm oil pressure a tad.