2002 GMC Sierra what could be the problem?

Transmission problem
2002 GMC Sierra V8 Four Wheel Drive Automatic

My 2002 gmc sierra 2500hd 8.1lLwhen I shifted it from park to drive the gear indication light was not lit like normal. I drove to the store and back and it drove as normal with no problems however I did notice it didnt illuminate(indicate) the park(P) when I got home. Upon leaving again it did indicate the R(reverse) gear but when I put it into drive it shifted very hard almost with a jerking motion. Immediatley the service engine soon light came on. I did drive it down my street to see if it would still drive, it never shifted out of first gear. I did get under the truck and noticed a lot of slush/ice around the sensor plugs. Any advice as to what could be the problem would be greatly appreciated. P.S. There were no signs or symptoms leading up to this incident.