2007 Dodge Grand Caravan 3.8L won't shift going uphill

My 2007 Dodge Grand Caravan with a 3.8L engine won’t shift going up hill. On any incline, it stays in the gear it was in when the incline starts and will never upshift. So we’re stuck going 20 to 25MPH up hill. Once we get to the crest of the hill, it shifts to the next gear and we’re good to go. From a standing still on flat land, if I nail the accelerator pedal, it also won’t shift, I have to back off the accelerator, and it will upshift normally. What’s up with this?

Have engine light on and the code indicates a bad EGR valve, and possibly a bad catalytic converter, but Autozone indicated that a bad EGR can also produce a code for a bad catalytic converter. They recommended replacing the EGR valve first, then see if the code comes back. But they didn’t know if this would cause a loss of torque, which might be related to the shifting problem.