slapfour

I have an 89 GL. It leaks out of the front main seal and the oil filter fitting, I think. I am not too concerned about hte leaking yet, but I am concerned with the oil pressure being over 75psi. When I start it it jumps to 45psi which is normal, but about a block down the road it is at 75 to 85 psi. I believe that the high pressure is causing the leaking. Can anyone help me diagnose or alleviate this problem?