Hey, my oil pressure in my 4age and my dad's 4age is unsually low as well, his is a new rebuild and mine is 175K km, it comes up and stabialises at around 3700rpm, i think they are all low. Think that your relif may have been a little stuck and now it has free'd up with exercise. I used Penrite 20w70 oil and it didnt seem to make any difference at all, so who knows,,,there strange engines.
Hope this halps a little