I was on the way home through the highway today and something weird happened to my automatic transmission Chevy Trailblazer (2017) 2.8 Automatic, diesel.

1. I believe I was shifting between gear 3-4 (approx 60KM/h). And the car was hesitant to shift (the RPM was fluctuating between 1500 to 2300 rpm, (i did not force the car to shift up) ,therefore I turned the hazard lights on and moved to the "slower, 3rd lane" lane. I was assuming the gear was slipping between gear between 3 - 4
   
2. I was looking at the side mirror and I saw "white smoke" during the incident above. Also there was a soft "grinding" noise during the incident above.
   
3. I got off the highway to stop in order to smell the exhaust. The smell was ordinary, soot smell.
   

I then decided to the service/frontage road to head home, and since this is Manila, top speed outside the highway/expressway is 40 Km/h or 25 miles/hour max (I assume the (Vehicle was shifting between gear 1 to 3).

Since the vehicle does have deep stick for ATFs, I crawled under the vehicle , removed the transmission fill cap, insert a piece of paper towel and I believe there are still ATF fluid, though its light brown in color.

The vehicle has about 105k KM / 65k Miles on the odometer. The rear axle fluid has also been changed.

The engine oil/filter is frequently changed along with the fuel , air and cabin filter.

The coolant has also been flushed and changed 2 years ago.



I have never changed the transmission fluid (since the manual states, it has "lifetime transmission fluid") but I am planning to change the ATF soon.

IS this a solenoid issue? or something else?