At idle, there should be no boost. At 1500 it will depend on the load and grade etc. Boost helps the engine build the power needed to get truck going. I can be running down the road at 2k, 70mph with no boost. Then need to climb a grade and boost could be a few psi to 20 plus with all the variables. hope this helps. Please fill in signature line so that we know what year truck and basic equipment to be able to better help in the future. Plenty of help and info available for the asking.