My trans was rebuilt with parts that greg recommended including one of his 2600 stall coverters. At very low rpm, there is a vibration from the trans. My builder advised for me to put the trans in neutral and slowly raise the RPM's. The vibration gets a little worse until about 3000 rpm. Do i need to worry about this vibration? I was told that the converter may be slightly out of balance? Does that make sense? Any other suggestions?