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.