Supercharged Gt Running Lean & Hesitating,help!

I've got a 2003 mustang gt with a Vortech V2 charger with a svt focus pump,42# injectors,lightning maf,k&n filter,ngk tr6 plugs,4.10 's as well as KB boost a pump.

I went to get it tuned at my shop a bit ago and it ran very lean and he couldn't make any power from it because of it,made barely 340rwhp and that was pushing it.I know most non intercooler setups can push nearly 400 easily.But what is causing this lean and hard hesitation.I get crazy hesitation once I give slight throttle,it just completly bogs down and goes no where until the rpms build a bit.

I've taken it to a closer shop which it currently is at and they're checking it out and seemed to be hitting a wall,they arent really sure what's causing it.Could it be my fuel pressure regulator?he seems to think that might be it but not sure.Do you guys have any ideas what it could be or if it's happened to anyone please chime in.

I've changed plugs,made sure a fuel line was pinched when I installed the pump and cleaned the air filter,easy things to test.Anyone got anything?

Ps the car has 90k miles on it

No I didn't do that,I read you could twist the 2 wires and short them out and it'd constantly be on or something like that.It's been a while since I did it so I don't remember exactly why it was done but I read it on quite a few forums to do that.Does that sound like it'd be causing hesitation?because I believe I got the bap after it had been hesitating but my shop seems to think this is the problem too

It goes learn nearly instantly,I'd say around 2k rpm and if I try to step on it a little hard like say for merging it goes --- on my wideband.

And to trinitygt that is what my shop was mentioning.No idea how I missed that part of the install,it's absolutely necessary for the install?but its sounding like that's causing it,but I went to get my car tuned about a year ago before my BAP and we still had lean issues although I dont recall hesitation

It's been a while since i bought it,don't recall the site.But it was the correct number when ordering and I matched the picture up with ones online when I received it,it was the green top.

Took it to my shop and he informed me my bap wasn't installed correctly,he fixed it and changed fuel filter and it seems to be running much better. Haven't gotten to test it completly yet.He also says running my wideband from my mid pipe which I did and just removed an O2 could be causing some of the problems too because my previous shop most likely didnt turn off the rear o2,does this seem right?could it be causing a lean condition?

Also he mentioned while it was on the dyno just for diagnostic he saw over 400rwhp,that's over 40hp more then I peaked at during tuning so that's a good sign