With engine running. I ll definitely check filter. I was running truck with stick pushing gas pedal last 500 miles between 50...65 mph .. going up hill speed was dropping to 50..than I heard engine running harder and up on 65 it was switching to quet run ...and so on ... OD button stopped working about 1500 miles ago alone with fuel light on and emergency break . I was told this truck didn't run long when I got it..month ago ...had to change rotor and caliper on passenger side and put new muffler Caz old one had holes in it...and about 500 miles ago ..harmonic balancer pulley started to spin on it rubber base ..so had to change that..Caz that belt was pulling waterpump and altinator. Now. Some squicking noise coming from engine area ...probably staring pump Caz belt seems shaking. . And I did cut air conditioning belt to see if that's airconditioner ...it wasn't. . So...now..not totally on a side of a road ..it parking lot of a store ..I can get all kinds of tools... and oder parts from napa and o'reilly.