I was driving my '02 TLS this morning to work at a constant 42mph. All of the sudden, the RPM drop to 900, then quickly spike back up to its normal level. It did this 3 or 4 times in a row. After that, it behaved normally the rest of the way to work. The ride home was flawless.

Is this a transmission issue? Has anyone encountered this before?

The car has 48K miles, and is 3K miles into the 2nd transmission.

Thanks.