[BrianG]

I'm pretty sure that your 'knocking' issue is just piston slap. Those engines have short piston skirts and tend to rock a bit inside the cylinder until warmed up. I know this is a real big issue with the 5.3l. I could be wrong though. Here is my thought. If the low pressure wasn't an issue until the mechanic touched it, then I'd want to know what he might have done to the motor to cause the issue. It sounds to me like you are really just paying for some one else's mistakes. I'd be talking to management and starting to demand that you won't pay if their work don't fix the issue. They can learn to play with motors on their own time.