Help! I have an 03 Malibu. 3.1 liter. I noticed a collapse vacuum line ( the u shaped hose on the PVC tube) I replaced it. Now it shifts from first. Then revs high like it is slipping (but it is not), and softly and very slowly shifts into second. After about a week or two it clears up. If you disconnect the battery and reset the computer it goes back to acting up.
This has been true for several months. The other day I cleaned the egr plenum because it was stopped up ( got a cel). I d/c the battery to clear the code. It has went back to shifting odd now and won't clear up. The car now throws a code saying the egr sensor is faulty. But the engine runs smooth, has plenty of power. Just the shifting issue.