Does anyone know the difference between 155 and 175's with fuel pulled out on a dyno?
I would assume that most tuners are pulling fuel out on anything above 155 with a stock turbo. If that is true (not saying it is) then you will probably end up with the same horsepower and less smoke with the 155's. Larger injectors put more fuel into the combustion chamber, increasing EGT’s. Larger turbos will add more air to keep the EGT’s manageable. On a stock turbo which is pretty much maxed out with stock injectors, there isn’t really more air available. So, tuner will pull fuel out to manage EGT’s.
If you were looking to do a turbo sooner than later, then 175's would be a good option, but it not, 155's will be a good size for a stock turbo with very little to be concerned with.
Fuel Systems, as Countryboy07 mentioned, the Trusted Performance stuff is very nice. If you are looking at doing 155cc injectors, the stock pump may be able to keep up. So, I would recommend upgrading the lines to the front of the cylinder heads (their Stage I) and a fuel pressure gauge. As long as your fuel pressure isn’t dropping, you are fine. If it does start to drop, then I would look at a FASS or Airdog pump and add a crossover line to the Stage I. (If you opt for 175’s you will more than likely need the fuel pump. Still watch your gauge, but plan on a pump.)
If you opt for 175’s, you may want to consider a water injection system. These systems add extra oxygen and cool the charge air temp, to help manage egt’s.
Head Studs, that is pretty much a loaded question. A stock truck can and will blows the head gaskets. So, if you plan on increasing the horsepower, heat inside the combustion chamber, etc, start saving for them. Can you get away without, depends on what day your truck was built.