Nissan Repair: hard shift, throttle position sensor, nissan altima

Question
Hi what would cause a 99 nissan altima automatic to shift hard only on the first shift and not the rest?

It only does it when it warms up, not when it's cold.

Thanks

Answer
sorry lots of possibilities

possible transmission flush, what is the condition of the fluid

possible defective throttle position sensor throwing your shift pattern out of range

possible defective shift solenoid

I would recommend taking your car to a transmission shop or dealership.