I have a 2006 M35X with 30,000 miles on it. The tires are new, I have new brakes, just-turned rotors, and the alignment is fine. When i am accelerating very gently up a hill just under 40 MPH using pure AT, I get this awful (albeit short-lived) shudder, which then disappears. No vibration. Same can happen on the freeway at about 60 MPH, but not often. Only happens going gently uphill, never downhill or on flat terrain, and if I use “manual” mode and keep the tranny in 3rd, it does not happen. Never shudders otherwise.
One possibility is torque converter clutch (TCC) chatter. I’d especially suspect this if the occasional highway event is under similar acceleration conditions, and is partly supported by the fact that you don’t get it in third. The idea would be that the TCC is having trouble unlocking.
It is due for a transmission service anyway (pan & filter every 30K is best). So I’d pull it into a good local - non-chain - transmission shop. Have them do a pan & filter service, describe the problem, and have them scan the computer for trouble codes. If you come up with any codes you can post them back here (the exact code) as there is a transmission expert who come through these boards fairly regularly.
I’ll check it out…
Had the transmission fluid flushed and replaced. Maybe that will help in the meantime
Was it just a machine flush? What you really want is to get a new filter on it and have the contents of the pan inspected for debris - meaning someone should pull the pan.