WOW, sounds scary!
Brother of the Benz, Jivesh.
It doesn't sound good.
If it were me, I would use an external oil pressure gauge attached at the oil pressure sending switch fitting.
This would tell you what the oil pressure actually is.
A drop in oil pressure as you are discribing could indicate major bearing clearance problems.
Are you positive of the oil level?
A low level and the oil pump sucking are reacts in the same manner as you discribe.
How about the oil viscosity?
Try the maximum straight weight oil suggested in your owner's manual. Possibly a straight 40W.
Remove the oil pressure regulator and inspect the springs for proper lenght and compression.
Make certain the regulator plug moves freely in the block and it's own piston.
If the oil pressure test substanuiates your condition, take it to your favorite shop for further testing.
Your reserve fuel indicator bulb is accessed by removal of the instrument cluster.
Happy Trails Beep Beep from The Spiderman in Hoiustoin!!!