If you're only getting 5psi then you've definitely got some issue's... . they should not be hard to find either...
First, pull off all the intercooler boots... . go over them up close and personal... roll them between your fingers like rolling a cigarette... look for cuts, 'rub through' etc... also look for signs of dry cracking like a tire get when left sitting in the sun unused for years.
Next, if all the boots are good and all your clamps were tight reinstall the boots, tighten them really well and pressure test the intercooler.
You'll need a piece of heavy rubber hose the same diameter as the turbo air intake. Slide that over the turbo inlet and, on the other end you'll need a plug/cap. This cap should have an air fitting and a small gauge.
Pressurize the system with no more than about 20psi and go looking/listening for leaks. It is normal to have some slow leakdown... all the valves in the cylinder head are not closed at the same time so some leakdown is normal but you should not have a noticably fast/consistent drop in psi.
If you do, you've got an intercooler leak(s).
As for the turbo itself, it is at fault I'm pretty darn sure you'd hear/feel/sense that issue very clearly. It can be checked by pulling the air inlet from the front of the turbo and, grasping the nut on the shaft end then moving it side to side, then, front to back.
There is a very modest amount of side to side that is acceptable but not enough to allow contact with the inside of the turbo housing wall. If it make contact then the turbo is on the very failing which is usually a very unpleasant experience.
Look for signs of contact. When you do the test fire up the truck for a few minutes and let the turbo bearings get well lubed, then shut down and do the check.
As for 'front to back' movement, there should be NONE !! If there is, you need to tear it down (or have it done) and install a new turbo "cartridge" or, rebuild kit.
Even a stock 1st gen turbo should be able to produce will into the mid/high 20 psi range when you have enough fueling so look for turbo/IC boot/IC core pressure loss.
After that, you can go on to more testing if needed but I think you'll find your problem fairly quickly.
If you have any guages maybe you could provide some info on your EGT's, smoke levels etc... that will also help the guys get you on track.
pb...


