Weird Problem...please help

I'm having issues again. Once you try to give the XJ some gas, it feels like well the cat is clogged or when the CSS is going bad. Rough idle, hesitation at 2,000rpm and beyond, like it's going to die. The CSS is new as of Thursday, and the cat has only 15k miles. I have check vacuum lines (could have missed one), the TPS, MAP, and the cap and rotor. Any ideas? I'm stumped on this one because everything that has caused it to do it before doesn't work now to fix it.
My lease is up on the car Friday so I need the XJ to go back into DD status for a few months again. Thanks, Juice

Juice, when you said CSS, did you mean CPS/crank position sensor?

Regardless, this sounds like a fuel system problem to me. I'd home in on checking the fuel pressure. A pressure reading would tell you a lot. I'd suspect the FPR or fuel pump. Probably a bad pump.....

Ya, the CPS. I replaced the pump last weekend but because it was down and out. I might not have gotten it right inside the tank. I'll check it out tomorrow and give an answer. The fuel pump when right in the tank without to much fan fair, figures never easy. Thanks, if that isn't it any other ideas?