360 has a low cyl

And if #5 intake lobe on cam, went really flat, might be a cause for 90 psi ? ateam

Yes, a worn lobe will lower compression pressure...

I would first take off a valve cover and crank the engine over and look to see that all the valves were opening fully... If you see one that is not opening all the way, then pull the intake and inspect the lobe...