90 astro/oil pressure problem??

When i start up my astro, the oil pressure guage reads high, but after 15 minutes it has dropped to a small box above the red, as in it had dropped almost over half of when it started off. Now i had this engine rebuilt 40 thousands over, its a 4.3 I had a leaking valve cover, but i tighten it down a little and that has stopped, the oil pump was brand new, just dont know why the pressure guage drops like it does,

might be nothing more than the oil pressure switch - the sensor that sends the signal to the gauge.

Mine used to bounce all over the place, till I changed it out.

Hi Kings
My oil guage readings bounce a lot also. It's steady at crusing speed, but at idle it bounces way to quickly to be the pump. It vibrates.
does this sound like the sensor to you?

Sounds exactly like what mine did. Fortunately it's not a particularly expensive part.

Thanks Kings. 1 more question, since it's cold and wet outside, I'm assumming that the sensor would be near the oil filter?

If it's like a 92 it's located right behind the distributor. It screws into a brass fitting that screws into the block.

Yup. what Champ said -
Be careful when removing the sensor so as to not damage the brass fitting

Thanks for the info