Great job! Breaking 50 is nothing to sneeze at.
Look into Pulse & Glide. That's where most of my gains are. Also, your tires are really hurting you. You don't have a scangauge? Get one. If you're getting 50's without, you'll do even better with one.
Look at my gaslog and note the tanks where I got the scangauge (jump) and where I started really using P&G (another jump).
My drive is about half 55-limit highway and half 45-limit city.
Oh, and this:
http://www.autospeed.com/cms/A_110216/article.html
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