2000 Sierra 4.3, P0300 No power

[bopell]

I have a 2000 sierra 4.3 129,000mi with absolutely no power. When the loss of power began,it took about 200 miles to become undriveable. Code P0300 random misfire. Fuel pump was replaced six month's ago. I have just installed new fuel filter, air filter, pcv, dist. cap, rotor, plugs, wires( I did find one that was bad). New MFI injection setup and EGR valve. It idles rough and when I try to bring up the RPM's quickly, it bogs down. When I put it in gear, no power at all! fuel pressure at rail...59-60. vacuum test off brake booster hose 13 steady, not the 16-22 I should have. I'm thinking a plugged cat. any suggestions what to check next?

[maxwedge]

Welcome to AF. Try disconnecting the exhaust in front of the cat, or check the temp in front of the cat vs the outlet, should be 100 degrees difference, if not it could be bad. Also 65 psi is the desired fp. If the vacuum drops way off under load the cat is usually bad. Does it misfire at idle?

[bopell]

Thanks for your reply. The vacum did drop way off when I tried to kick up the rpm and it does misfire at idle. It does seem to smooth out at a higher rpm but getting it there while in park is a challenge and impossible in gear. I did look for a thermometer(really had my wife look) but didn't find one. I'm going to drop the "Y" pipe with the cats tonight...I hope! I'll let you know what I find. Thanks again.

[bopell]

Yep, Left side plugged up tight. cleared the cat and it runs fine. i'll be installing the new one this week. Thanks for your help