I have a 99 Dodge 3500 24V Cummins and yesterday I had a shop replace my Hydro Boost unit. Everything was fine with the old one but I had P/S leaking out the weep hole.
Anyway, now it seems that the brakes will not release when I’m braking in a turn (like pulling into a parking lot or driveway. Once the wheels get straight it lets go. My mileage has gone from 19MPG to 14MPG. Could air in the brake lines cause this?

 

Nope, air would do the opposite, cause a soft pedal.

Betting the rod from the hydro to the brake pedal is too long, but just by a little bit. Do you have any free play in the pedal at all?

 

Only about 1/4 in play. I did just notice as I walked around the truck after stoping at a rest stop is that the brake lights were on all the time. I can pull up on the pedal and they go out. If I try and use my foot to pull up on the pedal after I release the brake, the truck is fighting against me pulling up on the brake pedal.

 

Take it back to the genius that replaced it. The brake switch needs replacing as is non readjsutable.