My H3 used to get 17 mpg and just resently dropped down to 13 mpgs, does anyone have any suggestions?

 

I'd start with the usual suspects. Check & replace air filter if dirty, check & clean spark plugs, tire pressure, fuel injector cleaner, etc. Then if it's still getting poor mileage, at least you know what's not causing it.

 

Thank you for your thoughts, all of that has been completed, along with transmission fluid. My next thought is having the MAF sensor replaced, this is the sensor where you connect after market computer power chips. Thoughts?