RR 3.0 Td6, 2004

Some 6 years and now 76000 KM ago, my gearbox was rebuild and I also installed a new TC (said to be a reinforced one).

In september 2020 (5,5 years and 65000 KM after rebuild) I flushed the gearbox, installed a new filter (non genuine...) and filled up with the correct Texaco ATF.

About half a year ago (so after the flush and filter change) it started with a hardly noticeable rumble (cattlegrid) at around 50 KMH . Seldom and mainly when cold. Also in very cold conditions this winter, I had hardly any drive because the box in D would not change up to second gear. When in manual no problem with changing up gears.
Now in warmer conditions the rumble seems completely gone, but now I have hardly noticeable fluctuations in RPM: mainly when cold and at around 80 KMH.

Could it be that my TC on its way out or could it be the non genuine filter (letting too much or too less oil pass trough...)? I might think that the TC should last a bit longer than only 70000 KM........

Many thanks for your guidance

Morning, the 'driving over a cattle grid' under acceleration sensation you're experiencing is quite often associated with lock up clutch problems. However perceived wisdom is always to do a box oil and filter change before committing to taking the box out.

Speaking from personal experience I had exactly those symptoms on my own 2007MY, but before I got carried away with the spanners I performed an oil change using a genuine filter. Result, all symptoms gone and greatly improved shift. I then carried out another oil change about 10k later, and that was it for another 40k until i sold the car.

While I'd agree, it does seem a bit soon to be getting these problems, I'd say it well worth performing another change using a genuine filter as it could well save you a hefty garage bill.