One problem related to transmission gear slipping has been reported for the 1998 Chevrolet C1500. The most recently reported issues are listed below.
Transmission code 1870 slippage failure, shifting from 1st to 2nd gear. Transmission bangs into 2nd gear. After reading web sites, it appears that this is a prolific problem with any gm transmission in a light duty truck. I've talked to other people in the area, they also experience same problem. Indications from web responses indicate could be electrical oriented by not confirmed. Rebuilding may not provide cure. Gm needs to own up and recall.