I have an 06 lt. 2.2 multi fuel. At 35 to 40ish mph it shifts in and out of overdrive. Any ideas what can be causing this? There are no error codes and all trouble lights are off

 

Normal shift point for 4th gear or OD and the torque converter locks up at that same time.

Try a full 30 minute battery lobotomy to reset the computers, simply disconnect the negative cable in the back at the battery, while it’s disconnected, check the TCM for bent pins or loose wires. Then reconnect the negative cable and take a test drive.

Notice , I typed negative terminal at the battery! Nothing under the hood!