Noise

1997 chevy balzer 4.3 6cyc oil pressure drop from 40 to 10 and making a knocking sound no loss in power About 3 weeks ago had oil change and new oil lines and gaskets put on because i had some leaks no noise or problems then just was losing oil then this happened first of all does this sound like a main bearing gave away second should i go back to where i had this work done and complain could they have done somthing to cause this they are very good and honest mechanics and a reliable auto repair mechanic company the blazer has 180,000 miles or do you think it just because of the milage it was bound to happen i hate to blame somthing on someone if was just a coincidense but does this sound like the main bearring?

Yes, this sounds like a main (or rod) bearing has been starved of oil.
Tell me more about this “new oil lines and gaskets”? What’s up with that? Unless your Blazer was turbocharged or supercharged you have no “oil lines” except those built into your engine’s internals.
By the way, have you checked your oil level since the Blazer was worked on?

With only the information provided, it’s not really possible to assess whether it was due to happen or the work done had an impact. Do you regularly check your oil level? How much were you using when you had the work done? Did you have any signs of extreme wear, like an oil light coming on at idle?