Can synthetic fluids really gain me 1+mpg?
 

Don't usually ask goofy questions like this, but i just changed out the axles, t-case and trans to Amsoil in my Mega. Just routine maint. Haven't had a full tank to calc mileage yet, but have gone thru over a tank since the change (several partial fillups).
Truck currently has 12k mi.
Over head has gone up from 19.6 or so (which is actually about 18-18.5mpg) to 20.6, same driving, same route.
Did I really get an additional mpg by changing out the fluids?

I believe so, yes.

I gain 0.5 just by changing the fuel filter and by changing over the Amsoil Heavy Duty Diesel & Marine 15W-40 oil.

I have seen some increase in economy, as much as 1.4mpg increase but it doesn't stay like that for long.
I have been using Lucas Long Grain oil and have great results with it. My 07 5.9 get around 23mpg on the highway and 18mpg in the city.

Absolutely yes.... and if you enhance some of them with friction modifiers you can gain even more. Rear end, engine, synthetic grease in U-Joints, etc. Add fuel additive and make sure you behave in a way that gains mileage... (like not idling for 15 minutes while it warms up, hot rodding it from stop lights, passing everyone in front you on the freeway just to have them pull up along side at the offramp stop light, etc.) You gain a bunch. work on that exhaust system too, it's worth about 3 mpg saved.

I switched the engine to schaeffer's supreme 9000 and gained .5 to .8 mpg. The diffs and x-fer case didn't make any difference they come with synthetics but I'll do tranny in 7000 more miles.

???The factory gear lube is synthetic???

Factory gear lube is a GL-5 rated synthetic...

That might just be enuff justification for a straight pipe:cool:!

?
 

can you be a lil more specific here?