This is not unusual especially with a new truck. Things like parking on a slight incline will give the sending unit a false reading and it will adjust accordingly as you drive. For some reason this design is very sensitive
I would do your own check with miles driven and gallons used when you fill up next.
2000 F-150 XLT Ext Cab. 4.2L V-6 153K miles
1992 Explorer XLT 4x4 5 speed stick 229K miles
1970 F-250 Camper Special 390 Auto 293K miles