So for a few months I had been having intermittent "lurch", or clunk, or hard jolts, whatever you want to call it, in my 2005 X5 4.4i. Relatively high mileage car--almost 100k miles when it all started. I took it in to the dealership, to get it fixed before my extended warranty ran out. They checked the transmission, and could not find anything wrong. They said no error codes read out. They offered to sell me a new one----NO THANKS! They did tell me the name of their recommended transmission shop in town.
So, I take the car to the transmission guy. After a test drive, he doesn't think anything is wrong with the tranny, either. Or at least, it is mild enough to wait until it is worse to bother taking it apart.
I mention all this to a friend of mine, who ran his own transmission shop for years; now retired. He immediately asked if I had changed the spark plugs recently. I admitted that it had been recommended at the 100k mark, but the service advisor also said I could wait a while longer, if I wanted to wait.
I took the car back to the dealership for spark plugs, and

the "lurch" disappeared!
My friend saved me from a needless transmission repair bill. If I had allowed the dealership to do the spark plug replacement when they suggested it, I would have saved myself significant worry and irritation.