There is an odometer module that looks as if it has failed. Mine failed at 70,450 miles and the car was due in for its 70K service so it was fixed at the same time (cost about $225). If you don't get it fixed without delay your dealer will be required, under federal law, to put a sticker on your left front door frame stating that the odometer was replaced and the mileage is unknown (not too good when you sell your car). Remember that on the 96's and up the actual mileage can be read through the OBD2 socket, no advantage to leaving it unfixed.
John Scales, (850R 1996)

It's totally electric, no cable to plug/unplug and if the speedo works then it's connected to the speed sensor. First try resetting the trip meter button (just a guess) but it's possible that there's a problem that might require a new speedo head (guage) and yes, call the service writer ASAP.

Also, as for your other question, if the compressor's cycling (clicking on/off) at higher rpms it's usually caused by low freon and maybe they didn't put the correct charge in?