Some ideas for my 1500

[90plow]

I have a 95' tbi 305 v8 4x4 1500 shortbed with an auto tranny. I want more power and better fuel mileage (better than 11mpg highway) So far I have added, a K&N air filter, cat back exaust, TB spacer, and a Hypertech performance chip. A cold air intake is probably something I will add unless you guys sugest against it. Other things I was thinking about puttingon are headers but, want to keep it legal with the cat. Which headers do I need to fit my stock CAT? (full length, shorty headers, which diameter?) I was also thinking about putting on a Gibson cat back because mine is just about shot (which may be part of my fuel mileage problem) I was reading about the B&M performance shift kit for auto trannies. Does anyone have one or know if its any good, its supposed to make the transmission shift better and harder and prevent slipage. Here is the linkShift kit (http://www.truckperformance.com/products/?searchtype=56d&sortorder=ADAAA&productcategory=Shift+Improvement+Kits&category=Drivetrain&sf1=GMC&sf2=1995&sf3=C%2FK+1500+Pickup&sf4=Vehicle+Specific+Kits)

Thanks in advance
Eric