Some Improved Gas Mileage - New Plugs and New Coils

I replaced the plugs and coils. This is a car I got for free and have no idea when the plugs and coils were changed. It has 220K and the plugs still looked pretty decent when I pulled them but went ahead anyway. I was potentially the second person to change the plugs and coils. as the plugs I pulled were not original. They were Bosch and replaced with Autolite Platinums
I had to drive a solid stop and go expressway, then over a very hilly road with a pretty steep climb.
I put 83 miles in and I went from 46.3 mpg to 50.1 mpg. I will put 250 miles on going from San Jose, CA to my home near Yosemite, so it will be interesting to see if the difference is maintained.