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97 Olds Bravada Suddenly Bogging Down/Not Shifting well

I have a 1997 Olds Bravada with 170K miles. Engine was running fantastic up until three weeks ago. Suddenly engine is “bogging” down and transmission is shifting between gears at certain speeds (like it can’t decide—usually around 40mph). Replaced catalytic converter because mechanic said it was plugging. Now engine seems even worse—it feels like it is working really hard, like the brakes are stuck on or like it is pulling a really heavy load. Gas mileage is worse. Trans is still not shifting right…at 40 and 50 mph it can’t “decide” what gear to be in and switches back and forth, and at higher speeds it has slight hesitations, like it’s “missing” or not getting fuel for a split second. Mechanic said it needs a tune up.

Background: Replaced transmission one year ago with remanufactured trans (could all-wheel drive be stuck “on”?). Replaced catalytic converter. Also just had A/C recharged and began using it about one week before these troubles began. I have stopped using the A/C in case it was related, but the problems have continued. Thanks.

Any trouble codes??


Nope. All my vitals looks good - no warning lights on. The RPM gauge does oscillate when the tranny is having trouble shifting, but otherwise holds steady at 2-2.5 when it finds its gear.

It sounds as though the TCC is falling in and out of lockup. Several things can cause this such as the TPS or even a faulty brake light switch. I would have a trans shop put a scanner on it and see whether the TCC is being commanded on and off by the computer.


Thank you! Do you think it’s okay if I keep driving it until I get it figured out?