Serious decrease in MPG....PLEASE HELP>>!!!

[interbizman]

Hi there everyone...
My truck.....2006 Chevy Silverado, 4.8, 4x4...190,000km....or about 115,000 miles. Im totally a novice at engine tuning..i know engines...but have never tuned so go easy on me...lol

I bought the intune 1000 for my truck in hopes of a perking up the engine and picking up a little gas milage....well...normally my truck got about 18 in the city, and about 23 on the hiway...now im getting about 12 in the city and 20 on the hiway...substancially down from where is was.
im from canada, so when im talkin about mpg its in cnd miles...not usa...your gallon is a little smaller than mine. so....when i say im now geting only 12 mpg in the city....its like you getting 9 mpg in the city....i dont see how its possible to have a modern 2006 truck that is in great shape, running very well with clean oil, new irridium plugs and a k+n filter to dump gas into the engine that fast.....
i notice my cooling fan is on alot more now and my gas guage is more accurate...but as for power and economy....so far i cant say i have made any gains....
what have i done....well...i have successfully downloaded the correct softwear updates...and installed them ..i have talked to some people about fuel slope adjustments but i have no idea what that is...
so i kinda neen some help here...i thought i would get noticeable results with this tuner...especially in fuel economy....
im not hoping for massive changes but at this point with the huge decrease in economy im hoping its somethign i did or an adjustment in fuel slope....what the heck is fuel slope anyway...lol
yes....i read the whole post on fuel slope adjustments in this forum...
thx....any help would be great

[mikel]

aftermarket tires/gears on the truck?

[interbizman]

stock tire size....265/70/17 on front and rear.
i think the gears are 3:83....at 98 kph or about 58
mph im running about 1400 prm on the hiway

[interbizman]

well...thx for all the help and support...im glad i spent 400 bux on somethign that didnt work ...