Need more info. How much more RPM are you gaining with less gear under you? I would pick the higher vacuum reading. Either way it's not going to be much mileage savings at all between the two.
Vacuum gauge is old school. Nothing wrong with old school except a vacuum gauge is not very accurate compared to a TPS reading. A vacuum gauge is to a ruler what a TPS is to a micrometer.
Bottom line is this. The best mileage you will get is the lowest TPS setting with the lowest RPM. Where those two lines cross will be the best mileage you can get is achieved.
There are a lot of things to achieve better mileage.
#1. Tire pressure to max pressure.
#2. Get off of the gas early when you want to stop. This is really important when towing to save fuel.
#3. Both pedals kill mileage. Any time you are on the brakes you are losing fuel mileage. Stay off of the brakes as much as possible. Any time you are on the gas you are losing mileage. Any time you are one the gas quickly you are losing even more mileage.
#4. Go as slow as you can or want. Speed kills mileage by 4X's.
#5. If you can pick a day with little to no wind do it. If you can pick a day with a tail wind so much the better. (I know most of the time you can't pick but if you can, do it.) A head wind will KILL mileage big time.
Above all:
#6. Fuel is cheap right now. Go on vacation!! :)
