You didn't specify which engine you have. So I listed available engines here - 4.3L and the 4.8,5.3,6.0L Gas motors have a minimum spec of 6psi at 1000rpm and 18psi at 2000rpm, and the 6.6L diesel has a 7psi idle and 28psi at 1800rpm. That being said - 20 psi is good. 20-40 is usually a good number at idle - it will move up the engine speed.
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You didn't specify which engine you have. So I listed available engines here - 4.3L and the 4.8,5.3,6.0L Gas motors have a minimum spec of 6psi at 1000rpm and 18psi at 2000rpm, and the 6.6L diesel has a 7psi idle and 28psi at 1800rpm. That being said - 20 psi is good. 20-40 is usually a good number at idle - it will move up the engine speed.