I have an 2010 g37x and have a slight shutter in the transmission. Car has 110k. This only occurs when I am doing about 80mph let off the gas and apply slight pressure to the pedal. It then cruises but has a slight shudder. If I press harder on the gas (not floor it) or let off all the way it goes away. It only occurs under slight pressure. Any ideas? Already have new plugs, new differential fluids, and new transfer case fluids. About to do the transmission fluid in the upcoming weekends.
thanks for the help!

 

If so, it may be a universal joint starting to go. If that's the case, it normally happens in harmonics, so you will see it at 40 mph and then again at 80.