Last year I had to have the motor replaced in my Trans Am... freshly buil Pontiac 400. Thought the mechanic I took it too was good. Took over 3 months to pull out the old engine busted motor (hole in number 8 cylinder wall) and put the new one in... even though he had the motor within 3 weeks. I thought it was running fine and even drove it up to and back from Atlanta and around town. Then it started running real rough and belching out smoke. Great... thought I had a blown head gasket because it was losing radiator fluid... but no signs like fluid in the oil or oil in the antifreeze. Got it to another mechanic and turned out to be a bad heater core.. which we blocked off until I can get the money to get it fixed. But thats not the worst of it all... turns out the car was timed incorrectly and the distributor was on wrong. I asked how far off it was and was told it was 180 degrees off... basically timed like another car. No wonder it was running bad. Now it is all fixed and running like a champ... just got to replace the warped headers (new mechanic recommended manifolds instead of headers) and fix the heater core. Would manifolds be better than a set of block hugging shorty headers?