The check engine light and trouble code indicate a problem in the transmission (as if you didn't know!). What needs to be done is to get the trouble code out of the ETC, which is the transmission control unit. The engine control module and ETC kind of work together to inform you there is a fault in the other system. It would make more sense to just have a seperate transmission fault light, but that's OBDII for ya!
You may need to visit the dealer to get the ETC codes read out, not sure if this is true or not.
There are a few things this sounds like to me. One is a bad rpm sensor in the transmission, which is part of what is called the "conductor plate". If this is what it ends up being, there are a few update parts which should be installed, but they don't get done "automatically", so let me know if this is the case and I'll fill you in.
Another possiblity on a 98 would be a part in the shifter called the "range recognition switch", these can both cause various complaints similar to what you have going on.

Gilly