See this thread:
https://ecomodder.com/forum/showthre...ods-32386.html
My previous Honda had an oversized motor and really short gearing. I tried all sorts of aero mods and it didn't respond well to any of them, because most of the losses were in the drivetrain. Sounds like your truck may be the same way, though to a lesser extent. Aero mods will reduce load but if your gearing and engine are eating up fuel you won't get as much from other mods.