infamous low oil pressure, but how low is too low

[HVY84CHVY]

this is my first post, and i figure i might as well get right down to it. i have a 98 sierra 1500 with the 5.7. i know that they have low oil pressure to begin with, but mine starts at 40 pounds when cold start, but after it warms up and gets to temp the presuure drops to about 20 pounds on the highway at about 2100 r.p.m and then at idle in gear it drops to about 10 pounds. when teh truck runs for a while and is shut off then is started less that five minutes later the pressure sits at about 5 pounds with the check gauge light on but when you tap the gas the pressure sits at 15 pounds. i am trying to avoid the fact that the main bearing need to be replaced due and was hoping that it was a regulator and clogged pump? anyone else with this problem or did i get that one lucky truck. also does anyone know if the 383 stroker upgrade is worth it?