Hello, i recently brought a 2004 Chevy 2500HD with 200,000 miles on it. I changed the oil and filter and replaced it with 5w30 high milage oil and it is fully fill. Then i noticed that the oil gauge is at 20 when start and idle but did goes up when step on gas. Some forum suggest doing a engine flush then drop pan and change the oil pickup O-ring. Some say the oil pressure sensor filter might be clog. Hopefully not bad oil pump bc that would be an expensive job. Do you think 5w30 was too light, should have gone with 10w30 or 5w40?. Any thought on how to fix?

Thank you