A vacuum gauge is one of the best economy additions you can make. Back in the day some manufacturers, like American Motors, put them on their vehicles that were intended for high MPG. They really help you understand what your right foot is doing.
Rusty: '81 F150 Ranger XLT 4x4 w/a 351M, RV cam, Performer carb & intake, C6, & 3.50's
Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads, Weiand intake, Street Demon 750/ZF5/3.50 gears w/Kevlar clutches
Big Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Worst fear: I die and my wife sells my rides for what I've told her I have in them.