Limp mode on a automatic

Firstly, disconnect the battery and leave it for a few hours. Reconnect and try the car again. This resets the memory in the TCM. If the car picks up the faults again, it will go into limp mode again after a short while. If it's been a while since you changed the fluid, then put some seafoam transtune in to clean all the parts and plates. Then after a few days at least, preferably a week, go for a fluid and filter change. After this, you'll probably find it will go into limp mode again, just disconnect the battery again and reconnect after a few hours. I had the same problem in my chrysler T&C. I left seafoam in it for a week and it cleaned up all of the gum and varnish build up on the shift solenoid pack and plates.

If the problem persists, and after you find it allows you to change gears for a while and then goes into limp mode, it could be gummed up solenoid pack, or input speed sensor.

Go to o'reillys and plug in their diagnostic tool. It should provide you with the fault codes if any. If no codes, then your TCM and ECM are in good shape, and if you're lucky then it'll be something simple like a sensor, or solenoid. Try cleaning it first with seafoam transtune in the fluid for a week.

If all else fails, and their are fault codes, then take the car to a trusted transmission repair shop for a road test. The computer could be picking up slippage and making the car go into limp mode. This could be the clutch plates if no errors with the TCM, ECM are present, and you've ended up checking out the input speed sensor, and solenoid pack. The latter can cause hard shifting and slippage too, if the seed sensor is set to signal when to change gear, but the new oil, or old oil have made the friction slightly different to what it is used to or within factory limits. Firstly try reseting the TCM by disconnecting the battery for a while and see what happens.

Good luck