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Hey everyone. I have a unique one here, 2008 Silverado had a backfire issue. When it would go into 4cyl mode and as soon as it would go back to 8cyl it would backfire. Run great other then that, done all the normal checks, plugs, compression ,fuel pressure and so on. All checked out and no ses light. So I tuned off the AFM with HP tuner and done a VLOM mode consisting of cutting the tower gaskets and blocking the oil feed to the VLOM with a bushing like what crazed performance repair uses . Note I have done this tune and VLOM mode over 30 times with success on many 5.3 engines. This time I lost oil pressure on first start up after the modification. The day before the truck had 40-45 cold 30-35 hot and 30 in gear. Done the VLOM mode and first stat up I noticed it was barely 20psi and at 160 degrees it already dropped to almost 0. No engine noise, drove the truck and it runs fantastic now but has the pressure problem. I checked pressure at the sender location with a manual gauge and it in fact is low, around 5 pounds, 1500 rpm maybe 10. Checked it at the block plug in front close to the oil pump 50 psi on cold start then drops to 30ish when idle goes down to normal, hot idle it is at 12ish but when revved the least bit it will raise quickly to 30-35. I cant get myself to believe this is coincidence of something falling that immediate .Is it possible a lifter is loosing oil pressure at the tower? Thanks for any input and I will post what the problem and not leave a open thread so everyone can benefit.