oil pressure problems

I was on my way home from work today and was watching my oil pressure guage. I have 2 of them a mechanical autometer guage and the factory one in the instrument cluster. They were both sweeping back and forth from 50-60 at hywy speeds. When the car was stopped and at idle they both would drop down to around 15 If I was driving and would floor it the pressure would drop and then climb up. I have a high volume oil pump and it normally sits at 70psi at hywy speeds and 40 at idle. I just had a the block and heads at a machine shop for new bearing seals and rings. I had a busted main cap that they replaced and they said everything besides that looked good. I have roughly 800 miles on the motor now. Any suggestions would be great.

No it has never done this before except the night back in January when I think I busted the main cap. But the 6-7 weeks I have had my motor back no it has never done this until tonight. I have been speaking with the machine shop for the past month about valvetrain noise that I have had and since have replaced lifters pushrods and rockers and its still noisy. I had Ford look at it and a performance speed shop and they said something is definitly wrong just not quite sure what. Both of them suggested that if one of the caps was broke maybe the block internally was cracked somewhere and thats the reason behind your valvetrain noise because oil is not fully pumping up all the lifters. Its falling back down thru the crack and back into the oil pan. Therefore you would never see it externally leak anywhere and your oil pressure would be fine because its measured down lowin the blockbefore it reachs the lifters and valvetrain. But then tonight all hell breaks lose on my way home from work and the oil presssure is sweeping back and forth and after the car sat for about 10-15min. I pull the dipstick out to check my oil level and its not even registering on the dipstick. I just checked it Sunday and it was fine and now its way low and its not burning oil that bad and the car and motor are bone dry on the outside. I haven't spoke to the machine shop today at all since this happened. ButI spoke with them once again yestarday and asked if they magnafluxed the block and he said no and then I gave him the other peoples theory on the crack block and thats why I have valve train noise and he said you can take that trheory and throw it out the door that the block aint cracked. He says I either 'aint adjusting it right(I've only been back thru it 10 times and that isn't exagerating) or I have some bad lifters even though they are brand new. So with that all being said who knows if they will help me out or not. The whole s#itty part of this is they called me and asked if I had access to another block when they found the busted main and I said no and he said that he was going to put it in the tank and see what the extent of the damage was. I found another block and called him back the same day and told him I could get another block and he told me lets just wait and see what the deal is with your s before you spend anymore money. He then a few days later told me it would be O.K. to use mine. And I agree I think if there's any internal damage that it should be on them but after him knocking off 400.00 off the total bill to help me out because I was short on money who the hell knows. The other thing he may try to say is that I ran nitrous on it which I didn't but I asked him a couple of weeks ago if it would be alright to run a 75 or 100 shot in it and he said I wouldn't your clearances are very close. So like I said I never did hook up the kit I have but if he remembers that phone call he may try to say that caused the damage as an escape goat. Hell who knows I am just so fed up with all this. I know when this started today the car seemed like it lost some performance to it. It just wasn't as peppy as it was this morning and when I first left work today. Maybe its just a bad oil pump but I doubt its that simple.

anyone