Tranny thump

[Sniper92]

So my 07' 6 has been doing this for a few months now...

Not all the time, but about 90% of the time shifting from 3rd to 4th I get a huge thump from my transmission.
Sometimes also when accelerating it will jump back a gear (which i understand depending on how hard you're hitting the gas it should), but I could barely have my foot on the gas and it will jump into the lower gear and accelerate really fast at a super high RPM.
Like I said before, the car will give a loud thump, and jolt forward very fast.

I saw something online not long ago that said these transmissions have to be flushed every 30,000 miles. I bought the car with 45k on it and flushed it around 56/57k and that was the original flush.

Any ideas? Is it fixable or should I just sell it?

Thanks.

 

[silntalrm]

Im not too familiar with the ATX in the 6. What year is your car? I would check engine mounts just to see if they could be.making.this transmission issue worse. Post on 6crew.com if you want more mazda6 guys to see this.