Nah....i run 60 and accelerate about normally. 97 ext cab long bed with an E4OD and 4.10's, 2wd.
I will say there were a couple times i got disgusting mileage. Usually headwind related.
Coming back from up north with my trailer loaded to the gills with wet pine trunks and the bed loaded to the top of the cab with various chunks of firewood, running in a 55-60mph headwind running 70 i got 6.2mpg. After i slowed to 60 it went back up around 10
But thats a rarity. Even towing my camper with O/D off, ac on, 65mph id get 9.
Average towing i get 10 all day