Without knowing all the details such as; mileage, type of driving,(stop and go or highway) , was the car ever in a flood etc. it is difficult to give an accurate answer. You say the engine idled fine between 17-18 psi but dropped off when you accelerated. It sounds like an intake leak.
I remember when I was doing this job I forgot to put the upper intake manifold on ( it was hot and at the end of a long day). I caught my mistake before I tightened all the bolts, but if I hadn’t caught the error it would have caused a leak.
That is a last resort option. I would check all the vacuum lines and connections first. Make sure you have connected all sensors, and double check the EGR solenoid make sure it is bolted on tight with no leaks. I hope this helps.