Rough Idle / boggin down / No Power

[norkiega]

Car - 95 Z28 LT1, everything is stock except for new cat back.


Problem - Up until a week ago the car ran great, but all of the sudden on cold or warm startup its runs rough like its got a big cam in it or somthing. You can feel the entire car bump once every second. When driving it, as soon as I hit 2k on the tac (for lack of a better description) the car shudders... or boggs down all the way through WOT. Like its starving for somthing. I almost left this important piece out. The night before this all started happening I ran the gas tank low. Not out of gas but I wasnt sure I was going to make it to a gas station. I did and topped her off.


What I've done so far - After reading tons of posts here I replaced the fuel filter and it didn't matter. I checked the fuel pressure with the following results: Idle in park 35lbs - idle in drive 36 lbs - in park tap the gas jumps right to 42 lbs - take her for a ride and any time my foot is on the gas its 42 lbs and at WOT 42 lbs. I left the guage on overnight and noticed the pressure backed down to 0 lbs but as soon as I turned the key it jumped right to 42lbs and started right up. It always starts fine. I checked and there are no codes in the computer.


What should I check next ? - I had an 85 Z28 with a clogged CAT and I could have that sucker at 4k on the tac and it would only go about 15 mph.
I'm leaning that way on this car but I pounded on the cat at seems rock solid.
I dont want to spend the money on a off road y pipe if its not going to fix the problem. Any ideas how to test the cat??????

Any other suggestions as to what to look for would be appreciated!!!!!!