looking for more mpg or power or both
 

so ill start with HI, im new this is my fist post so be gentle.

i have a 1999 z71 ext with 5.3
k&n cai
mass air flow sensor
tb spacer
gay tornado
shorty headers
77 flomaster dual no cats
6'' fabtech lift
35x12.5x20 toyo mt with 46,000 miles and counting still has a good 15,000 left on them, i'm very surprised at the amount of mileage I've gotten.
4:56 gears ( rear only the guy is supposed to install the front in a couple weeks.
hypertech lll programmer ( crap power) better mileage horrible shifting
crane cams programmer (awesome power, awesome shifting, bad mpg

so what im wondering is why i hear or talk to people that get on average of 15 mpg, and i get 12.5 mixed easy driving.
and also i just bought a boat and the truck seems to pull it very good off the line but dies in power as you shift up. normal??
another thing that i have noticed is that if I try to drive easy and go to pass someone without down shifting, as i push on the gas nothing happens and ill keep pushing then all of a sudden it just takes off like a beaten dog. what would cause this. i should be able to accelerate without mashing the accelerator that hard right?

any and all help will be greatly appreciated.

Is your check engine light on? When was your last tune up?

Yes my check engine light is on. Along with ABS light. Had o2 simulator installed after headers. But didn't notice the truck running different. Tried putting the o2 back in and sims out and nothing changed. I feel that my truck is fast. But when I have 4:56 gears and can only chirp the tires. Something not right I had a guy who has an identical truck almost minus all the bolt ons and he said my truck is a terd. He said his 5.3 could walk on mine and he also runs 35" tires.

oh and yes ! i had it dyno tuned. took it in because i had a sputtering issue. the hooked it up to the computer did a couple runs gave it back and it ran good.

it's crazy there are so many different opinions out. as i read 50% say no cats is good, and the other 50% say that it makes the truck perform worse.

i just want more torque than i have now. and more torque should save me on gas. at least i would think get me moving easier that is for sure.

thanks for the reply to nullhead

Get rid of the Hand Held programmer and get a real tune done. I know I got a hand held programmer too, but I also only have a 2 wheel drive... less weight. Also get rid of the TB spacer. Waste of time, unless it is drilled and tapped for NO2. Short tune headers are a NO go, Long tube is the way to go. Also the true dual for a stock motor is killing you... not making enough horse power to run duals. Go back to a single in dual out. Also how are you running a tornado with a CAI? Bad mileage could be due to the gearing and the tires throwing off the spedometer...

Run a cat, with a single pipe to a dual out muffler, with stock manifolds or headers - your choice- ditch the spacer, programmer and maybe install a higher ratio gear in the rear end.

Also, get that check engine light figured out.

so what it sounds like you all are trying to say is that I do not have enough back pressure. correct ?

and i have read that the shorty are not as good as the long tube but they def. have to be better than the stock.

and i would like to get a custom tune done, read that wheatley performance is good and they will update it for free.

there is a gear calculation you can find on line somewhere where you can plug in the make and model tire size etc etc etc and it will tell you the appropriate gearing to set to back stock.