It seems that several owners of this kit are not seeing the 7 PSI boost that myself and others are. I like to keep things simple when troubleshooting, leaving the really complex failure modes until the simple stuff is ruled out.
The simplest explanation is that the boost gauge is reading incorrectly. I bought a cheep manual gauge two weeks ago to verify the boost on my rig, and it correlates to what the 14 in one gauge is telling me. 7+ PSI max (saw 7.6 PSI under full acceleration over the weekend, for just a second)
The next simple explanation is a boost leak. The compressor housing to the center housing is a possible leak path. There are only four connections after the turbo before the TB. Then you have the TB gasket to the upper intake, then the upper intake to the lower intake, then the lower intake to the head. There are numerous ports in those assemblies to look at, including the EGR, brake booster (should have a check valve from kit), and the PCV valve . The PCV should act like a check valve under boost. It could possibly be leaking at higher boost levels and dumping the boost into the valve cover? Then it flows back to the intake side of the turbo?
(Side question, with a large boost leak, isn't the turbo being turned at higher RPM's due to the wastegate not opening, as it is not seeing a pressure signal to open? Is over speeding the turbo a risk with a boost leak?)
Another simple explanation is that the wastegate is opening too soon. You verified you have the correct springs. The next step would be to pressurize the wastegate manually and verify that it is opening at the correct pressure. Probably not likely that the correct springs are out of spec, but, maybe?
On the exhaust side of the turbo, as you looked into, a restriction could be putting to much backpressure on the turbo, causing lower flow, lower turbo RPM's and less boost. You could also have a large exhaust leak, but, I think you would notice that.
Hope this helps,
I regularly am seeing 6.1psi, with the occasional blip to 7.
I was seeing higher consistent boost levels loaded down pulling grades.
If i'm empty and flooring it usually only see 5 or so since the motor isn't under enough load to boost to 7 before shifting.
This can be a lot of things.
is the truck driving normally turbo aside? Throttle position sensor functioning properly and adjusted correctly?
Holding gears properly? Trans kickdown adjusted properly?
I replaced my upper intake manifold gasket and TB gasket last weekend since i was seeing some signs of seepage at the joint of the upper and lower intake manifold and a slightly high idle.
Afterwards I wasn't seeing as high of boost and truck wasn't downshifting well or building as much boost. Pretty sure i need to tension the trans kickdown up a bit to get back to where it was.
Think of simple stuff.
Rule out the gauge first, and verify that it actually reads 0 at ambient for your elevation.
Check for boost/vacuum leaks between compressor housing and block. All gaskets appear leak free?
Do some reading about diagnosing turbo systems online, pretty basic across all turbo vehicles.