I have been bothered from the first post , but rather reluctant to chime in.
The fuel pressure caught my eye. In a FACTORY EFI system with a fuel pressure regulator and return line to the fuel tank , the pressure varies. At idle and low loads the fuel pressure would be more like 28 psi and as engine load increases the pressure also rises by about 8 to 10 psi. That is done so the pressure across the injector remains constant. (delta is the term) The fuel pressure rises to match the increasing manifold absolute pressure. (decreasing vacuum)
The picture you posted shows a fuel pressure regulator with a small hose on the right side of the regulator. (passenger side) That should be your reference to the manifold pressure. To test it , you would pull the hose off with the engine running and fuel pressure would go up that 8-10 psi. The hose should be dry , any fuel and you have a regulator problem. There should also be some vacuum at the now removed hose.
I have zero experience with a engine with IR manifold and efi. I understand the "vacuum " signal can be erratic. (bounce around) Most manifolds have all cylinders drawing from a common plenum and one large throttle body to meter air flow. Manifold pressure (vacuum) is more stable .
I would look to see the small hose is connected to the manifold and in good condition (not rotten). It is possible the MAP sensor has lost it's connection as well if not bolted to the manifold directly.
I use the Harbor Freight contactless infrared thermometer for $25 . I use it for "looking" for heat in brake rotors and bearings. A industrial quality instrument has a correction factor that has to be entered for the material you are scanning. Copper vs steel vs skin vs what ever.
Another thought is a scan tool does NOT pick up all faults, only sensors that are monitored. It can not tell a clogged air filter or tell a bad plug wire from a fouled plug. They only point you in a direction.
Boss wrench has good advice , start with the logical and simple things and work your way throgh the problem rather than go full "Mike the Snake" mode.
I hope that is food for thought and wish you luck in your repair.
Please keep us posted.