1997 GMC Suburban Suburban WITH OIL PRESSURE PROBLEMS

Hi
I purchased a 1997 suburban with thw 5.7 vortec motor, has 216000 miles first thing I did when I purchase the suv was have the oil changed. Went to start in the morning oil pressure was at 40 drove it and started to notice that when I come to a stop the oil pressure would drop to 0 but when I press on the gas the oil presure would go back to 40 so a mechanic said to put 40 weight so when I change the oil I noticed metal shavings in the oil plug ( I think it was aluminum because the metal shavings were easy to bend). So I took the suburban for a test drive and it did the same thing but this time I hear a tapping noise when it goes to 0 oil pressure. So I'm going to replace the oil pump and since I was going to be down there I was going to replace the main bearings and inspect the crankshaft. My question is to remove the crankshaft do I need to remove the engine from the suburban? I look in the repair manual and that what it said dont know if they were talking about an overhaul. Any suggestion?