I'd try reading and resetting the check engine light and see if it comes on again.. to determine if it was a one time occurrence.
Don't know if your '96 is doing something my '85 5M Cressida would do, but driveline shock (flex) from hard umm...as in full throttle driving, <img src="/forums/images/graemlins/shiner.gif" alt="" /> <img src="/forums/images/graemlins/shiner.gif" alt="" /> would cause it to set the 42 and 61 speed sensor codes..
Driving on very rough roads with lots of power applied (or out of balance rear tires would do the same thing) could also set the codes.
I think they had the computer error tolerances set too tight for slight speed differences seen between the two speed sensors (one of the transmission) and the other in the speedometer.
Never had any problems with the entire driveline..
After you reset the error code see if they come back under other driving conditions.
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EDIT: I'm jumping the gun and assuming yours is an automatic transmission.. I should have asked as Azrain did below.... and the error codes would be important to know so, get those read and let us know...
If it's an auto, and you are concerned about it possibly slipping, the following summarizes from the Toyota repair manual the diagnostic procedure that a mechanic would do. It's called a stall speed test.
The basic procedure (with the vehicle and transmission up to operating temperature) is to fully apply the hand brake, step down on the brake pedal very hard to keep the vehicle from moving, and with the transmssion in gear "D", go to full throttle for no more than 2-3 seconds and quickly observe the maximum engine rpm.. It should not go above the torque converter stall speed which is around 2100 rpm. If it goes significantly higher, your transmission is slipping so let off immediately..
This must be done in a safe area in case the brakes aren't on hard enough to keep the vehicle from moving. And, under no circumstances should the throttle be down for more than 5 seconds, and if it's slipping, let off immediately. Otherwise you could further damage your transmission.
