At 131K you may be seeing some mpg loss due to drift on the O2 sensor.
Not cost effective to get back 1 mpg.


Jeff
96 T100 SR5 4WD Ext Cab, Warn Hubs, HD torsion bars, Bilsteins, Camper Shell, TJM bar, factory 31 x 10.5's, Powertrax No-slip rear, Recaro driver's bucket