Ejbresin

2017 Chevy Silverado 1500 LTZ - reversed out of garage into driveway (slanted street about 12 degrees) parked truck. Reversed into road, shifter does not respond to shifting to any gear. Checked linkage cable for play, all seems well there. Next replaced fluids in pan, fluids were a dark black almost like oil on fluid removal. No chunks of metal Found on bottom of pan or on magnets. Replaced fluids to procedure to proper temp and fill drain plug to a drip. What’s my next step? Possible solenoid issue? Valve issue? The truck starts and runs excellent but seems as if it’s stuck in neutral. I’m aware of the manny issues of this sealed 8 speed but don’t seem to find any troubleshooting with these parameters of being stuck in neutral.