One pipe hot and the other is cold!!!

The engine came out of a 70's suburban. Its a 454. I had some valve chatter that seemed to get louder each time I drove the car. I thought a lifter was clogged so I changed the oil thinking some fresh sythetic might clear it. The chatter got much better as I drove the car. Suddenly the engine quit for a second then ran fine. A mile later it got very rough with extreme missing. I had to put it in 3rd to keep up speed. When I got home I checked the coil specs and it's ok. I could still hear ticking under the drivers side valve cover. The next day I let the engine warm up and put my hand over drivers side exhaust and it was extremely rough and cold while the passenger side was even and warm.
Any ideas what my problem is.

Several questions. Is it a stock 454 or built up from OEM? If you didn't rebuild it how many miles were on the clock when you installed it? Have you pulled the valve covers to see if you have rocker problems? If it's an older engine, not rebuilt then putting synthetic in it may well have broken loose all kinds of sludge deposits that have now totally plugged your lifters. Just a thought.

Yup - what Roger said. The synthetic may have freed up a "mountain-o-crud" (highly technical term for sludge) that's caught heaven only knows where (my guess is valve train). I'd pull the covers and start looking there. You might also pull the plugs as they will tell you how things are igniting.

Good luck and let us know what you find
Glenn