I have a 1998 Chevrolet 1500. My service engine soon light is on. It has recently started running rough when I am coming to a stop. Acts like it is going dead.

The check engine light means there is a trouble code being set - have it read by a mechanic, or buy a scanner and read it yourself, or have it read for free at most any auto parts store. Once you know what the code is you'll have a better idea what is wrong with your truck.

Below is straight from the manual for a flashing and solid light. If you have an OBD II reader you can usually see what is wrong. If not I would take it to someone who had an OBD reader. Light Flashing -- A misfire condition has been detected. A misfire increases vehicle emissions and may damage the emission control system on your vehicle. Dealer or qualified service center diagnosis and service may be required. Light On Steady -- An emission control system malfunction has been detected on your vehicle. Dealer or qualified service center diagnosis and service may be required.

Here is a link for the manual or just search 1998 chevy 1500 manual in google. https://assets.gm.com/manuals/chevrolet/1998_chevrolet_1500_owners.pdf