PO300 chevy silverado

I have a 2006 silverado,55,000mi, w/t 2wd 4.3l v6 vin X with a poor acceleration problem. So bad I can barely make it around the block. Seems fine on cold start, but once warm, exhaust noise gets loud and almost no acceleration at all. The more you push the gas, the slower it goes. Had Chevy dealer tell me exhaust valve was burnt. I refurbished heads and replaced all lifters on passenger bank. Still same problem. Getting code PO300. The reason I replaced pass. side lifters is because lower intake has clean dry runners on drivers side, and filthy, moist runners feeding passenger side. Figured if it wasn't a valve, maybe a lifter was failing. No such luck. I find it hard to believe a cap/ rotor will fail for one bank only. There is no egr to stick open, and injector failure wouldnt cause filthy intake runners, would it? I'm thinking its a timing issue, but why only one side? Is there a hidden cam sensor even with a distributer? where do I go next?

Those engines have a ton of issues with the fuel pressure regulator failing and it will puddle fuel in one side of the engine leading to misfires on one bank, As well a plugged cat on one side is not uncommon on those trucks and it would lead to gutless performance! Fuel pressure is super critical on those trucks but Im betting the exhaust is plugged on one side or the 02 sensor is not switching enough

Thanks for the educated response. I actually started thinking it could be a cat... even with the relativly low milage. I unbolted the cat/crossover from the headers and took it for a spin around the block. Aside from pissing off the older couple down the road, it actually accelerated better, and even downshifted when floored, which it didn't do thru the cats. It still ran a little rough and spit out a code for the O2 sensor, but thats to be expected without a full exhaust. For all you out there with the same issues, I called chevy, and the '06 came with an 8 year 80K warranty on the emissions system. That means so long as I can get it to the dealership, diagnosis and repair should be free. Of course the last dealer mis-diagnosed and wanted to rebuild the top end (which I did myself for $300). But with the info I have for them now, should be relatively hassle free. I'll keep you all posted as to the outcome in a few days.

Nice call Jeff.

I just read this post and was thinking the same thing.

Yeah you've probably worked on more of them then me Mohawk but it seems logical and I've heard the trailblazers do it alot on one bank. Now to find out why the converter failled?