When pulling away at about 20mph, transmission dropped to 2nd, very loud bang.

Speedo to max, rev counter to max.

Gearbox is auto.

Any ideas ?

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1990 124, 300E 2.6 (daughter)
2004 Cayenne S, Fabspeed Cat Bypass, BMC Racing Filter
2000 Lexus RX 300 (Wife)
Retired 1999 ML430