I really haven't noticed much of an increase in mpg either, though my mpg is nearly the same now 16yrs later as when it was new, even though it has a higher drag coeficient and weighs over 1k lbs more.

To avoid the failure of most electric fans, i.e., the thermostat, I have mine wired to the ignition, so it runs all of the time. The dealer commented that it might prevent the truck from reaching its proper temp, though the gauge sits at the same point as with the belt driven fan.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed