1996 Ford F150 Owner's Manual - Page 109

Driving uphill or on a steep grade When the speed control is on, your vehicle may significantly drop speed when driving uphill, especially with a heavy load. If the speed drops more than 8 to 14 mph (15 - 25 km/h) the automatic speed control will, by design, be canceled. You may have to temporarily resume manual speed control while driving up a steep grade in order to maintain the speed you desire. Frequent shifting of an automatic transmission or speed loss during speed control operation can be eliminated by shifting out of overdrive into drive (or by pressing the Transmission Control Switch, if equipped). These conditions could occur in hilly terrain or at higher elevations. If the speed control "dropped out" after your climb is completed, the speed of your vehicle can be reset with the SET ACCEL switch, or returned to the previous set speed with the RESUME switch, as long as you are driving over 30 mph (50 km/h). 107