[Domman56]

Me and my friend Zach took his brother's 2002 GMC sierra to Simi valley to my sponsor to get his truck tinted since he was coming back from the army. We were on our way back and the truck had been doing great on gas since it's a V6 (vehicle was reading about 23MPG) I decided to try coasting down a few hills.
Coasted from 60MPH everytime i would let it coast in nuetral the fuel gauge dropped significantly once i was to the bottom of the hill. This doesn't happen when it's in drive though, i will say i forgot to check if the avg fuel economy on the trip went up or down from doing this but does anyone know whyy this truck would do that?
It'd be much apppreciated