My bonnie seems to shift into o/d even when the shifter is in d-3, and not in the o/d position, and at hwy speed under acceleration it will shudder until I give it enough throttle to kick it down a gear. I just took this car on a road trip this weekend and thought I may be possibly experiencing a fuel delivery issue as well.I loaded some STP injector cleaner before I left, as I have also noticed some shudder at low speeds as well. Any troubleshooting tips would be much appreciated, as this car is relatively new to me, and I plan to change the f/f first, and possibly the O2 sensor, because the car seems to run rich.
Thanks

sounds like a gear is slipping in my opinion. may need to take it to a tranny shop for a free estimate. but im sore some more advanced members will chime in and help with other great solutions...

Are you sure it'* going into OD, and it'* not just the TCC lockup that you're feeling as that fourth shift?

As a test, if you're driving down the road at around 55-65 in "3", and shift it into "OD", you should feel it shift, or hear the RPMs come down. If not, something is up.

It almost sounds like a TCC lockup shudder issue, though I didn't think that was very common at all on these older non-electronic transmissions. The lockup was very abrupt on these things. On newer models, they made it a smooth engagement, and as a byproduct, introduced more slippage... and wear.

The shudder at low speeds: Do you mean at about 35 mph, and again at about 45-50? Those would be speeds where the transmission has just shifted into a higher gear, and so the engine isn't revving very high at all. If you are in need of a tuneup, you will feel some shudder or surging at these speeds. If that'* all it is, new plugs and wires (if necessary) might solve that issue. Might solve the high-speed problem as well, if the transmission is working properly.