The engine is not performing efficiently, possibly because of plugged or restricted injectors or high altitude conditions.

Refer to Symptoms in Engine Controls.

The converter parts are broken.

Replace or rebuild the converter assembly. Refer to Allison service manuals.

The vehicle stalls at speeds of 50 percent of normal, which implies a freewheeling stator.

Replace or rebuild the converter assembly. Refer to Allison service manuals.