all stangs will drone at 1800-2k
the only mufflers that literally almost dont drone (they all do somewhat) are glasspack race mufflers like magnapacks and dynomax race bullets
you are asking for it on the highway.
I have gotten over 360 miles on a tank of gas with my 3.73s
try tuning and setting up your car instead of giving up performance
and for anyone that thinks turning 2500 is high on the interstate... have you ever driven any other car other than a muctang, save for a pickup truck everything is going to turn at least that for the most part.