I just rebuilt the motor in my truck,everything new except Cam & Cam Bearing...When U crank up it has about 30 pounds of oil pressure,then as it warms up the oil pressure drops dangerously low...

Wow. Everything but that huh? Galley plugs? Lifters? Is the teardrop oil feeder from the block too shallow? I mean did you resurface the block and now the port is too shallow to get the oil thru? Did you adjust the lash in the rods? After adjusting lash, did you turn the rocker nut one half turn to set the lifters? Oil pump? Type of oil used being a rebuild? Bored out? Need more info. Trying to help because tennisshoes is right about sabotaging your rebuild. Thats like throwing a bbq and forgeting the beer. Might have screwed the pooch on that one. If you plan on removing the valve covers again, inspect the cam for severe wear inside the journals and for christ sake, redo the bearings.

And another thing lol. Did you advance/retard the timing of the cam? If so, how much? And is it possibly an aftermarket cam? Hell man, dump MMO and Lucas stabilizer thru it if all else fails.

Pull your oil pressure switch and check for a screen in the passage it screws into. I have recently read the threads about these v8's and saw many discussions about losing oil pressure READINGS, but engine sounds good. Have you been in this port or passage and seen this screen to be clean ? You can also call GM parts counter to see if they have an update or procedure other than pick the screen out and inspect.