[ChuckS]

I have the Airlift 5000 with onboard compressor on my 2007 Duramax. In over 13 years of use I’ve never had to add air once I set the pressure where I want

I run 25 psi empty and 65 to 75 loaded....

You’ve got a fitting leaking. Bottle of water mixed with some dish soap makes a good leak detector Solution. Apply at each fitting, T fitting, and compressor feed line to find the leak