low oil press @ idle

My 4.3 vin. z ( 87000 mi) loses oil press.@ idle when eng. temp. reaches 220 degrees. The check gages lamp goes on and I feel a bump down on brake pedel W/noticeble loss of some braking effiency. (cold engine o.p is 45lbs w/gradual decrease as eng. warms to op. temp. ( mech.guage says 10psi oil press.) I have replaced : O.P. sending unit, eng.temp. sensor. pvc, brakes. (Also loses radio signal w/popping noise in speakers) Could it be caused by bad ground?? Any good electricians out there??!

I have a 1990 S-10 4.3 doing exactly the same thing. My idle seems lower than it used to be. I was thinking it probably just needed a tune up, but I haven't done anything yet. 122,000 miles.
I changed my oil to 20 - 50 w and that has helped some.

the weight of the oil really makes a difference? What is the best oil to use then?

The 20-50W oil is just a little thicker even at the higher temp. Since the oil pressure is better before the engine reaches full temp, I figured it would help to use the heavier oil. And it has, some.
It will make things harder on your engine in the winter, since the cold will make the oil even thicker. I think the book recomended 10-30. It really depends on how cold it gets where you live.

@ Idle, or even standing @ a redlight the oil pressure somtimes drops below 20 and the Engine light fickers, I am guessing the head on mine is got a suck Valve or somthine, but I have over 187,000 miles, I think I need to get a new 350 block and heads and start over!