1991 CHEV C3500 7.4L 4L80E. AT CRUISE 65 TO 70 MPH TORQUE LOCKS UP & UNLOCKS FEELING LIKE A SURGE. NO CODES. VSS, TPS & OTHER CONTROLS SEEM TO BE OPERATING NORMALLY SCANNING ROAD TEST. HAVE FLUSHED TRANS & CHANGED LOCKUP SOLENOID. FLUID SMELLED REALLY BAD BUT ... Login to read more.