I own a 2001 Chevy Malibu with a V6. The problem I am having is the engine is slightly revving up on the highway. It is most apparent when I am going 70mph. The RPM will be at a steady 2000 (at 70mph) then will jump up to about 2300-2400rpm for about 2-3 seconds and go back down. There is not pattern to it either. It may do it again a few seconds or a few minutes later. If I even stay a few mph under 70mph it seems to make a difference but after driving long enough (say 2-3 hours highway driving time)the problem will creep in while driving 60. At slow city driving though I have never noticed it. It also does not matter if the weather is hot or cold. Does anyone have any ideas or had this same problem?
Auto or manual transmission? It appears you are seeing a tach show an increase RPM do you also hear or feel an increased RPM?
If Auto I would suggest checking the fluid first making sure it is in good condition and full. With a 2001 car (what mileage) I would guess it is about time to change the fluid and clean the filter. If you have not done that, now would be a good time. Note. If it is the transmission, and if you do change the fluid, remember that the damage may have already been done. If it fails 6 months later, it did not fail because of the fluid change, it may have failed because of the lack of an earlier change.
It sounds like the torque converter locking and unlocking which can be a few different things. If you took it to a reputable transmission shop (ie not AAMCO), described the problem, and suggested that it was the TCC locking and unlocking, they’d know right where to look.