Are you "ABSOLUTELY SURE" that your engine is a 289 with a 289 crank shaft? If so, "HOW" did you come to this conclusion? I can tell you that when my brand new 1999 - 5.0 was first fired up, it had the correct 50-oz flywheel, but a 28 - oz vibration damper/harmonic balancer (not as my builder claimed) and the vibration was not very severe at all. I'm just glad that I tracked it down in the first 400-500 miles. I find it very difficult to understand how the transmission itself could be causing your vibration while parked in neutral/park. Even if the numbers on the block tell you it is a 289, there is the unfortunate possibility that at some time the engine was rebuilt using a 50-oz imbalance rotating assembly with the possible intention/assumption that it would make parts matching easier with the AOD. I am sad to say that the only way you can be 100% positive of the engine is to pull the oil pan to see/inspect the crank shaft. Trust me, I feel your pain and would really hate to see you spend the $$$$ on a new transmission to still not cure your ailment. I hate to it, but there is another, more insidious possibility that, during a down & dirty rebuild, only one or a few cylinders were over bored and fitted with mis matched pistons to get it "out the door" for quick sale. I'm sad to say that I've seen unscrupulous builders do this kind of crap before. R & R ing the oil pan is not a difficult operation, even for a "non-wrench" kind of guy.
