I found this and I think it would be very helpful, but I hope you ever need this.

Is about a P1870 DTC, related with tranny sliping

"What is causing that? Will a rebuild fix it? Or does this mean a new tranny? I've been having the transmission filter / fluid changed on a regular basis.

Also, does the code need to be clearer out?

I recommend taking the car to a reputable transmission shop and have them run it through some tests. It could be a lot of things internally. P1870 is a common DTC code on a 4T60E or 4T65E tranny and nicknamed by tranny professionals as the "Elusive 1870 Code".

It could be the TCC/PWM soleniod, TCC apply valve, convertor regulator pressure, the separator plate circuits, sprocket ratios, the turbine sensors, PCM ground, torque convertor, valve body, TCC circuit leak due to worn parts (turbine shaft) , etc. Any one or a combination could or will trigger P1870.

For now, you should reset the ECU and clear the DTC codes. Run it again and see if the code re-appears. If P1870 returns, the course of action is obvious. Good luck!"