2002 SLS, 110,000 miles.
For 2 weeks now, I have been getting bad readings from the speedo: digital reading jumps around, 17mph, 27mph, 20mph without much change in actual speed. Oftern reads low (in 40s on freeway, though keepiong up with free flow). Believe it has never read high. Transmission seems to "believe" the low readings, staying in lower gears up to higher RPMs than is usual. Perhaps I am kidding myself there on the "belief".

My favorite shade tree mechanic replaced the speed sensor (the easy one to replace, not the hard one). Also advised that he had added three (?!) quarts of transmission fluid. (This is the same guy who, five months and 4,000 miles ago, replaced TCC solenoid without it being a $1000 job. He solved my P1870/CEL/smog check problem with that)

Replacement of speed sensor did NOT solve the speedo&shifting problem. On a road trip last weekend, when first getting on freeway, the transmission stayed in a low gear up to redline RPM, and then shifted poorly and harshly. While cruising at 70mph (tho speedo read in 40s), trans would frequently shift, from top gear to the next (4th?) and back.

Only error code showing, whether current or history, is U1016. Still shifting a little harsh, and speed readings remain inconsistent and often wrong. Have my doubts about taking the vehicle more than a few miles from home.

What say the Wise?