Sounds like you need a
ScanGauge - then you don't have to "guess" about how well you're doing!
A note on aerodynamics: drag doesn't "start" at 60 mph. It's a common misconception, though. (Ride a bicycle and you know that aero drag is present - and a significant factor - even at 10 mph.)
As a proportion of fuel burned to move your pickup down the road, @ roughly 30 mph, 50% of your power is spent overcoming aerodynamic losses, and the other 50% is spent on rolling & mechanical losses.
Above that speed, the proportions continue to tilt towards fuel burned strictly overcoming aero losses.