Fueling & Injection - Help me with my fueling problem

First of all. My car is a 98ls1 with TFS 215 heads. Fast 90/90, and 228/230 cam with all supporting mods. While on the Dyno, my tuner was trying to make some fueling changes and could not begin to get enough fuel in. At WOT my car ,even though it is getting to open loop, never gets richer than bout 14;1 no matter what he tried. He said it has to be a fuel delivery problem. My question is, how to I determine if it is my pump or pressure regulator? They are both stock so I guess I was wrong when I said that I had all the supporting mods.

Did your "tuner" bother to check the fuel psi, while this was happening??
How about inj duty cycle?
A stock pump is not going to "cut it", with the changes you've made....
I doubt the injs will either, if they are stockers.

My tuner said it is probably the fuel pump. His dyno is leased by another shop. Can you believe that porshe tuning shop didn't have a fuel pressure gauge or they didn't want to let us use it and the tuner didn't have his with him. (bad move)
Either way, we checked it today on a gauge at his shop. It idled at 58psi and cruised at the same. As soon as I opened the throttle and loaded the motor, it drops to 50psi. That makes me think he is right. I know that 98s are bastard years and things are different. Will a 99+ pump work in a 98? The injectors are ford greentops, I think they're enough. I should have been a bit more descriptive in my first post but was in a bit of a rush.