Gentlemen,
(staubers and xterradon)
Please get a boost gauge. The truck does build boost (even in stock form) below 3000 rpm. The fact that is at hand are two things:
1. The supercharger is not spinning at enough rpm's to produce more than 5lbs of boost below 3000 rpm's. In stock form the boost will stay at 5 psi up to 3,000 rpms, from there it will build to it's maimum of 7 psi. After the vacuum line mod it will start at the same pressure, and build to a maximum of 9 psi at 5999 rpm. The rush you feel at 3000 rpm is partially when the supercharger has reached enough rpm to start producing more boost...Remember that the supercharger on the trucks is technically a compressor. All compressors have a rpm/efficiency rating, and therefore are not producing their maximum boost at all rpm's. To keep the compressor within it's maximum rating it will inherently have some losses at the lower end due to the wide operating range (rpm's) of the engine. The same applys for turbo's (a/r ratio), and blowers.
2. The engine is still camshaft dependent (just like many other cars), and to enhance fuel economy the cams are ground to provied good fuel economy at lower rpm's (where the sane minded people usually drive), and better power at higher rpm's. The rush you feel at 3000 rpms is the engine coming up on to the camshaft's designed torque/horsepower curve. If you would look at the horsepower/torque curve for the vg33sc you would see that at (or about) 3000 rpm's the horsepower is surpassing the torque, which means that the power is being produced at a greater rate - hence faster acceleration. If you were to load the truck (towing over 4000 lbs) you would not feel the rush, as the acceleration would then be dependent on the torque more than the horsepower.
I don't believe anyone here wants to go into the depths of torque -vs- horsepower...
That said, I have the same rush in my X at 3000 rpm's, as well as my 2002 v-6 powered F150 (company car) at the same rpm's...My mod won't help that.
Dave - I'll send you the pics for the mod if you do by an S/C X...