here's the deal. If you upgrade to a 75mm throttle body, and you have NO other mods...
you will get a little extra power, but eat up GALLONS more gas. not worth the upgrade by itself.
if you put on a the throttle body in conjunction with ALL the other bolt ons like the spacer, CAI, MAF, pulleys, GOTTs, tuner, etc. etc. AND port/polish your intakes and elbows. you will see an overall gain somewhere in the realm of a 2-3 mpg increase on the instant readout cruising at highway speeds.
the power is about 20-50 H.P. the reason I fluctuate the numbers so much is for one reason....the tuner. mild tune = mild power. and so on up the scale.
just make note that a 75mm throttle body WILL hurt gas mileage, but WILL make it faster (however it is only by a little) I personally have opted not to do a throttle body upgrade, I am trying to get this beast to do 20mpg @ 70 on the highway. I currently travel at a steady 18mpg sometimes 19mpg and get a little over 400 miles out of each tank of gas.
if the question is posed "Are you happy with your upgrades?" the answer is hell yes I am.
where as they say the actual gains may be minimal if you couple all those possible upgrades together you end up getting a pretty substantial and noticeable power,torque,& mpg upgrade. Not to mention you can feel it in your seatofthepants dyno. which as we all know is the only one that matters.
but to get the power you have to do all the upgrades, the MAF sensor lets the CAI work to max capacity. the spacer gives just a little bit better atomization that equals a little better throttle response. the exhaust lets all the extra gas breath easier from the truck. the pulleys take away parasitic drag from the engine, Efans remove it the rest of the way and the tuner helps all the other items perform top notch because the brain has now been made better. so it's a lot of little upgrades that equal the big noticeable change.
so sit down. work out a plan, and alwys keep your eyes open for the next helluva deal.
I cruise craigslist and ebay 5 days a week. in one shot...for $400 I was able to buy a magnaflow catback, superchips tuner (older but worked fine) K&N CAI with Granetelli MAF, and JBA stainless shorty headers.
in another steal of a deal I got the underdrive pulleys and the throttle body space for something like $100-$150 whatever half price works out to be.