Engine is not working as hard to hold 70 mph, rpm's are down at 70 75 80 is a characteristic I have observed post Boss. If its just me than me and not the boss then hats off to my tuner, freakin nailed it and he has his dyno dialed in. Car is also quieter and drones eliminated I keep winning with this boss install. Its jumping to the top of my favorite mod list.
What he was referring to is the fact that you have a manual transmission so vehicle speed will equal a specific RPM regardless of the mods you have unless you change gears or tire sizes. The fact that you have a new intake manifold will not alter RPMs in any way.