I've looked in the GM service manual. Nothing is mentioned about one bank being starved. I've been on this forum since 2003 and have never heard of anything like this.
I could say, remove the intake plenum, your valve covers and pull the rear hydraulic lifter and see if its dry. If you had a borescope, you could look into that bore and look at the oil out put hole to see if its clogged.
I doubt you will see much of anything. So really, your only option is pull the engine back out, pull the cam oil galley plugs out and find the blockage. I know you don't want to hear that, but I know the feeling and its hard work. I've had to pull the V8 out of my *-10 twice.
1997 Pontiac Bonneville SEi-SCRAPYARD
2000 Chevrolet Blazer LT 4X4 4.3L
2002 Chevrolet *-10 LS Ext Cab 4X4 5.7 V8