Loss of highway mpg

[demontang]

Ok got my custom tunes and Im running the 87 performance tune right now. I'm getting 13-14mpg intown running 30-45 mph but when I hit the freeway Im getting 4-8 mpg a tank even going do a steep hill it only reads 8 mpg?? Ive pulled the codes and only get p1000 and Ill get that cleared by doing the run cycle and after it sits over night that code comes back. Ill get code p0420 and p0430 once a week now which is because I dont have cats or maybe the O2 is going I dont know. The highway mpg has me confused though