I have a 335i with a 6HP21, and the converter lockup behavior was the first thing I noticed when I got the car. It usually locks up in first gear, which I’m sur

I have a 335i with a 6HP21, and the converter lockup behavior was the first thing I noticed when I got the car. It usually locks up in first gear, which I’m sure helps with fuel economy a lot. That said, the overall shift quality could be a little better, IMO. I’m no transmission expert, but I think it basically shifts “clutch-to-clutch” instead of using sprags like a traditional automatic, so it’s really sensitive to timings. If the second clutch engages too late, it’s in neutral for a bit. If it engages to early, it’s in two gears at the same time. For example, if you’re accelerating lightly and it’s about to shift, then you suddenly have to hit the accelerator harder, sometimes it feels like it has already committed to shifting under the lighter load and it almost feels like it’s in neutral for a split second before banging into the next gear. Not sure how much of this is related to the BMW shift maps or the transmission itself. All that said, the transmission has proven to be very reliable. People in the 335i community are putting well over 500 ft-lbs of torque through them and they seem to be holding up, and my car has 211,000 miles and it shifts the same as it did when I got it with 40,000 miles. Also, people with newer 5.0 Mustangs don’t seem to have many complaints, and it’s basically the same transmission.