Ive got a 01 7.3 4x4 with 222k on it. Recently my mpg has dropped from a average of 14-15 to maybe 9-10. I noticed that crusing speed (50-55 mph) that my boost gauge is barely reading anything. I went through today and checked all the boots and retightened all the clamps on my pipes. Went for a drive and stayed around 2-3lbs @50. That seems pretty low to me still.
I can turn my programmer up and floor it and it will jump up to 26-27 lbs, but qucikly drop once i let off.
Make you a boost leak detector. Go to the hardware store and buy you a 3" PVC end cap, and if you don't already have them, a threaded fitting that you can snap an air hose into and a tap so you can screw the fitting in.
The OD of the end cap is 4", so undo the end of your air intake line and stick the end cap in the hose and clamp it in place using the factory hose clamp. Then hook up an air compressor with the pressure regulated down to 5 - 10 psi. Spray all your connections or any suspect leak locations with soapy water and look for your boost leak.