97 GMC YUKON 5.7 4X4, HAS A PO785 CODE......WHEN FIRST STARTED IT SHIFTS AS IT SHOULD. BUT AFTER ITS WARMED UP AND I STOP AT A STOP SIGN I COMPLETELY LOSE OVERDRIVE AND IT WON'T DOWN SHIFT. I HAVE TO MANUALLY DOWN SHIFT. WAS TOLD BY MULTIPLE MECHANICS THE IT WAS THE 3-2 SOLENOID. SO OVER THE WEEKEND WE CHANGE THE 1-2 SHIFT SOLENOID VALVE, 2-3 SHIFT SOLENOID VALVE, 3-2 CONTROL SOLENOID AND THE TCC PWM SOLENOID VALVE. RESULT??? BACK TO SQUARE ONE, STILL THE SAME ISSUES DIDN'T HELP OR CHANGE ANYTHING AT ALL. THERE IS ONE OTHER SOLENOID THE I DIDN'T KNOW WAS IN THERE SO IT DIDN'T GET CHANGED. ITS CALLED A PRESSURE CONTROL SOLENOID VALVE. COULD THAT BE THE PROBLEM??? HATE TO WASTE MORE MONEY ON IT IF ITS NOT GOING TO FIX THE PROBLEM. NOW IM BEING TOLD THAT THE PO785 CODE MEAN SHIFT TIMING?? NOT SURE WHAT ELSE TO TRY OR DO. CAN SOMEONE PLEASE HELP????? EMAIL...... [email protected]

SOURCE: 91 gmc shifts in and out of overdive

I had an 89 Suburban that started doing the same thing. Change the fluid/filter and add a quart of Lucas Transmission Fix. See how that does. Ultimately, you are going to have to rebuild or replace the transmission as the problem will only get worse in the end. Mine finally went down completely and cost me about $2700 to rebuild.

SOURCE: 1998 gmc jimmy shifts fine through 3 gears wont shift into overdrive

check transmission fluid .

SOURCE: i have a 97 gmc jimmy 4x4. the transmission goes

I need the CODES this year has valve body problems for tcc slipping on these & shift timing need more information

SOURCE: 95 GMC Sierra 4L60E will not shift down to 1st or up to 4th.

no power stuck in 3rd gear electric shop unless youve burnt it up good luck...www.TransmissionGarage.com

SOURCE: 1997 transmission Slow Acceleration

not sure if this is the answer yet but i have the same problem with the same codes i work at an auto parts store and a few of the techs that are customers have lead me in the direction of changing the ignition switch, i am doing it today will let you know if it solves the problem