When you're cruising and you decel, what map reading do you get? If you're close to 10 or below it may not be tripping the dfco which would be the reason for bad gas milage.
You should be able to actually hear the tone of the engine change once it's hitting dfco. You can also monitor the dfco parameter to make sure it's activating...your wb should peg lean.
-10psi is quite a bit, that's approx -20 inHg... I'd be surprised if you're pulling that much vac on decel. Take a log at idle and decel and post it. Your decel vac is always going to be higher than your idle vac so it's a fine line where the dfco setting needs to be for it to work correct.
I'm out of town for a few days so I can't do the logs. However, on decel the vacuum may go to 15 inHg (is that about -7 Psig) around town. The only time I've seen it higher would be at cruise speed on a long and steep downhill grade. I haven't seen the AFR go lean for quite a while on decel so maybe that's a parameter that I inadvertantly changed somewhere along the way. I'll check earlier versions of my cal files.
