Some constructive feedback and opinions would be much appreciated on a recent transmission problem/failure I've been having:

After some spirited driving the other day, while going about 70mph in 4th gear at medium throttle, I tried upshifting, the indicator went to 5th but the car stayed in 4th, I hit the upshift paddle again to go into 6th or 7th and it continued to rev down from 4k rpm until I stopped. I turned the car off, put it into drive (no harsh shift or anything) and tried taking off slowly, but from 2nd to 3rd it locked up and revved to 3500rpm before slamming into gear making a noticeable thunk and the rest of the gears seemed very hesitant. I got the car home and let it cool down. Drove it later that evening very lightly and noticed no bad symptoms at all. For the next 3 days, I didn't notice a single hiccup from the transmission so I assumed it had just possibly overheated that day

Well tonight, after some driving that could be considered mild to semi-fast, the car did the same thing except the symptoms weren't as bad, after stopping, 1st gear felt like I was taking off in 2nd or 3rd... But it quickly went away as I drove the car very slowly. What could be causing this? Should I get my transmission flushed? Can the sealed 7AT be flushed? Am I going to need a new transmission??

Again the symptoms all seem to hit at once without any check engine lights: sluggish shifting/holding of gears, abnormal shifts out of normal rpm shifting range, no hard shifting from reverse to drive to neutral. Please help and thank you in advance!

 

How many miles on the clock

 

Also what year is your G and have you had any transmission TSBs applied?

The 7AT isn't sealed and is serviceable, the standard procedure is a 3x drain & fill, I wouldn't recommend a flush as this can dislodge debris that can get into the internals of the AT. Here's a DIY on the procedure and this also includes removing/cleaning the pan & magnets (which is also what I would recommend).
https://www.myg37.com/forums/d-i-y-i...rop-clean.html

 

It's a 2010 with 82k miles! I dont believe it has had any TSBs applied! Would a dealership be able to do this for me or would it be better to just go to a car shop for this? Any idea on the price?

But I completely agree, a flush is kinda harsh on the trans, did not know you can drain and fill! Any other recommendations?

It just hit 82k miles!

 

You'd have to go to the dealer, have them run your VIN# and they should be able to determine if the transmission has been updated. A 2010 probably has at least one update available. At 82k miles I would definitely get the 3x D&F and see how much they charge to drop & clean the pan & magnets (if you aren't one to DIY).

 

So while I'm waiting for my Tuesday appointment to have it checked out, can anyone tell me what the difference between a g37x sedan and coupe transmission is? Is there a difference? If I end up having to buy a new transmission, would I be able to pick up a used sedan trans?

 

The transmission itself is the same. They both run the same computer and Attessa-ETS, but as long as you use your cars shafts when reconnecting it, it should be fine. I am not sure of the differences in length, but I'm sure there is some. But first thing is to get the old fluid out. These trannys are a bit temperamental if not changed relatively frequently. My Honda was the same way.