why cant i run a 120 race on a early 99

[Power Hungry]

You'll be pretty happy with the Stage 1's, although there's no real reason to change the HPOP. In about 85%-90% of the trucks, the Stage 1's will run perfectly with the stock HPOP. Stage 1's use less high pressure oil than a standard AD-Code Split Shot. In fact, I've run injectors as big as 400cc on a stock HPOP (detuned of course) and had no problem maintaining ICP. One thing I will advise... If you think Stage 1's are going to be the last injector you plan to buy, then that's fine. However, if you're the kind of person who is hard to keep satisfied and will continue to build on your truck as things get a little boring, get the largest injectors you can afford and just have them detuned to meet your application configuration (HPOP, Turbo, etc.) as this will save you considerable expense in upgrade in the long run. We can easily change the tuning as you make subsequent improvements to the vehicle.

Take care.