6L45, 6L50, 6L80, 6L90, 6T70 (Gen. 1), 6T75 (Gen. 1). It is no longer necessary to replace the expensive TEHCM assembly to rectify this concern. Pressure Switch Rebuild Kit. If more than one switch breaks down, failsafe mode can be triggered.
GMC Transmission was sticking in 3rd or 4th occassionally - pulled the TECM and 3/4 disks were ruptured. Replaced them and it works great. Highly recommend getting the installation tools to go with these.