cheaper atf causes lower mpg?

[Bigsyke]

I had synthetic mobil1 atf in the tranny, drained and refilled twice with some cheap walmart stuff. Now it seems i ran almost 1/2 tank of gas in 50 miles?

I was getting 25mpg avg before. I also swapped in a new intake pipe to replace the OEM pipe. I had an AEM dryflow on before, these are the only 2 things ive done since the dramatic drop in mpg and performance.

[420sx]

theres something else to it, atf is atf for the most part unless you are running a 800hp + setup with a nasty tq converter and you need the extra edge. air intake would not do this either.