I have noticed that my turbo has dropped to about 3psi of pressure. I assume that the wastegate is somehow controlled by the computer and the 3psi is the fail-safe pressure. That said, I don't see any computer control on my turbo; the wastegate seems to be controlled by a vacuum regulator hooked straight into the intake manifold. I assume that if the pressure in the intake manifold (boost pressure) gets high, it forces the rod out on the regulator which then opens the wastegate. I don't see any additional computer controls.

What are the steps for diagnosing a turbo issue?

I have checked all of the vacuum lines and replaced the ones with issues

I get the 3psi turbo pressure at around 2500 rpm, and it does not increase with engine speed. If the turbo was seizing, I would think that at lower rpms, it would not respond at all.

There are no weird turbo noises, nor have there ever been any.

There is no smoke; my car passes an emissions test.

I have also inspected the inlet of the turbo; the vanes spin freely and they are not mangled. There is no contact with the housing.

The only weird thing is that in the winter, I get some obstruction in the intercooler; maybe it is a bit plugged.