Hi all,
this is my first post thought I'd give this a shot before going to a mechanic. I've got a 95 F-250 xl 4.9l straight six it's got 279xxx with a rebuild about 80k ago. Here're the issues:

1) hissing/sucking noise in cab, noise changes tone when brakes are applied. Have checked brake lines no obvious leak, no obvious fluid loss. Brakes work reliably though the pedal slowly edges down while engaged (it does eventually stop before it gets to the floor).

2) the more worrying issue: gasoline smell in cab. Checked the EVAP system, hoses mildly corroded but not broken. Smell seems concentrated near brake booster.

I read a post on a different forum referring to a similar problem in an 80's model Ranger wherein the FPR (fuel pressure regulator) was janky and allowing gasoline into the brake booster. Does anyone have experience with this problem on their own truck?

Also truck seems to have pretty poor mileage considering the engine model. Could this be linked?

Please respond with any comments, suggestions or criticisms/clarifications you may need.