Brake pedal not returning

[WH1_T-Type]

so this isn't the standard issue of a pedal not returning after pressing it.

Car is an '86 T-type with converted vacuum boost. Up until about a year ago the brakes were great. Things went south due to mice chewing things, I took it to a local mechanic (I live in the mountains) and they ended up replacing the booster and bleeding the brakes.

When I'm park it is 100% fine. As soon as I put it in anything besides park it will stay down until I hook it and bring it up.

I was thinking possibly the check valve on the booster, but why would it be good in park if that was the case? Nothing was changed besides the booster, so I shouldn't be having to add a return spring to the pedal as it worked fine before.

I don't have a crap ton of time to spend on this thing as the ship I'm stationed on is about to deploy....hence why I took it in to be fixed!!

 

[No disintegrations]

When the car is put in gear the drop in rpm can cause a reduction in vacuum. I'm wondering if you have a vac leak or something like that going on. Throw a vac gauge on it and read in park and in gear.