Engine stumbling and dropping oil pressure..

Ok, I have Dart mostly dialed in, it starts and idles great, however after the engine is really warmed up (driving around for more then about 20 minutes) the oil pressure dropps from about 50-60 down to about 40 when i am stopped, and when I try to start accelerating, it seems like it has to catch up with itself for and minute. However when I put the trans in either Nuetral or Park, idle stays the same, but the oil pressure comes back up. (PS it is idling about 700-750 in both drive and nuetral).

Second problem, when driving down a road at crusing speed (idle around 1500-2000) the car seems to be stumbling/surging if I let my foot off the gas, or get into it more, it seems to be fine.

I have checked vacum and at idle I am getting a reading of about 14.5-15 steady at idle. I have been reading about adjusting the vacuum advance by using a alen wrench and going through the vacum line hole at the front of vacum advance port on distributor, but I am really not sure that will help and I want to get more info before I start messing with that. I have tried running alittle leaner and richer and that doesnt seem to make a difference. I am going to change the plugs also. I have checked the timing in park w/ e-brake set and idle around 750 (is that right, becuase some say that way and others say with the idle round 2000 in gear, but for that I will have to put the car on stands becuase I think that would pull it even with the e-brake on)

Thanks