Well, since I am visual learner here's a site that carries throttle bodies: http://www.bbkperformance.com/products/throttle-bodies.shtml.  Basically these are like the butterflies you see on the top fuel and funny cars you see at the NHRA races.  They allow air into the intake to mix witht he fuel, some even release fuel.  I can't figure out another better way to explain them, the best thing to do is google it yourself. But it is a good way of adding 15-20 quick HP in gas motors.  

I also have a 96 F-250 3/4 ton.  I had start up trouble with mine... I live in Michigan where its not very warm for long.  I read in this mag that a good rule of thumb is to get the turbo exh. temp up to 300 before you take off running.. this I found is very true.  You may have some glow plug problems(dont forget those pesty valve cover gaskets and harnesses, they like to melt over time).  Also the very best and first mod. should be a set of gauges(exh. & boost).  I get roughly 14.7 straight highway with 206,000.  Well I do have a banks filter(stock box) and a 4" down pipe and 5" to the back.  The guy before me had the stinger kit put on it for pulling, but took off the chip and trans commander, and I still get 14.7 doing 80mph everyday.  The cheap stuff that people usually over look seams to be the most expensive mods to make. Like your turbo, check your down pipe for wear, and also your clamp. leaky pipes lose power like you won't beleive.  Also, if you haven't found a manual for your engine, its because most auto parts store don't carry it. You'll have to order one from Murry's, or Napa. Worst comes to worst, your local Ford dealer will take an arm, or leg(your choice) for this supplement book.

Good luck  

Do you mean city or highway mpg  if you mean mixed or city on a 4X4 probably the best you are going to get.  Anyways though about mpg i have a 1994.5 powerstoke (yes there are 94 and a half models very first ones) 5 speed 2wd extended cab long bed with topper and on the highway i can get 20+ mpg this truck has 360,000 plus miles on it drives like a champ will bury the speedo in a heart beat on the interstate still getting great mpg when you do have to do a clutch mine cost me about 800 dollars but the flywheel was original and if the clutch wasn't someone replaced it with orignal ford product! i only paid 3800 for mine and it has a about dent free glossy paint body for being 14 years old and you can tell it is orignal.  The thing is having a older beast like this might cost you some money and some sowntime but you own a first generation powerstoke which means everyone elses newer ones are based of ours and we have one of the most dependable ones yet!  The 6.0 was a disater and the 6.4 breathes fire sometimes and i have personally saw one of these and i have not heard any good stories of mpg. i can't keep from spinnign in the rain now so why do i need a chip!  that is just letting the clutch out no pedal i have to spin 1at and some of second to get in third and then if you aren;t careful i will brek loose some in third! anyways bear with i love mone and i think you will yours once you get all the bugs worked out!  

I don't know if you guys knew this or not, diesels don't have throttle bodies. There's no butterfly thingie between the air filter and the intake ports. Diesels' engine speed is controlled by the amount of fuel injected into the combustion chamber.

The closest equivalent to a throttle body on a diesel is an intake plenum, and a lot of companies make performance plenums for diesels. Banks is one of the best-known (but not only) company that makes them:

 

AFE STAGE II W/ PRO-GUARD 7

95 PSD F350 2WD SLIGHTLY MOD'D 325/685 AT WHEELS...AVG 20 MGP

GOOD LUCK WITH TURBO.  

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