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Basically what he is saying is that the PCM is making the transmission shift to 6th gear at lower rpms than it should. However, I don't think it is this simple. The manual transmission cars have the same problem. I can make mine do it at 2000 to 2200 rpms steady speed 30 to 35 mph in third gear. If I UP shift at that speed to 4th it drops rpms to 1700 or so and the vibtration goes away. I firmly believe this is a throttle position, MAP, timing and VVT tune issue. When you shift, either up or down, you force the engine to a different point on the tune table and thus it stops vibrating like my old Harley. Since both manuals and autos are having this problem, it isn't a torque converter shake issue either. The only other thing which could be causing it is exhaust reversion which would cause the AFR to jump all over the place when exhaust gases are reverting back up through exhaust valves, then intake valves and thus messing up in incoming intake charge. This is why I asked in antoher thread on this if anyone with long tube header (would change reversion timing or eliminate it) or anyone with a Trifecta tune is having the issue.
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