Scan Gauge will help a lot!
Shift right around 2250rpm
with a high throttle position.
Keep your top speed under 55.
With just a few aero mods you should be able to get into the high 30's easy. You can look at the progression of my fuel log and track mods that were done and how long it took me to get over 40mpg. On a pure highway trip, I should be able to get over 60mpg, yet I my fuel log shows 45mpg 90day avg. I'm trying to get a 50mpg summer avg. and it's not going to be easy. Your goal of 45mpg avg. will be tough unless you EOC. EOC makes everything easier. You'll need to delete you Power Steering to do it safely though. I recently did this and it is barely tolerable, my wife won't drive the car anymore.
Take a progressive approach when moding. Sure you can copy mods, like I did, that have proven to work on your car, but it helps to understand their interaction so you can make good decisions going forward. For instance. My grill is completely blocked. My radiator fan comes on every couple minutes...this hurts the mpg by a noticeable amount. The question I have is: "How little can I open my grill block to allow enough air to cool the engine and not cause the fans to come on while minimally impacting the aero benefit?"
You should consider things like this before jumping off the deep end like I have