2011 Silverado 6spd. Any opinions on transmission fluid change intervals? If so, what's the best brand, synthetic, conventional?

 

I would stick with the factory oil for that transmission. The idea with the oils used now a days is that they do not need to be changed as often. However changing them early is not going to hurt. I would probably do it every 25k or do them per the factory recommendations. Obviously in a HD or HP application you should service regularly. Not an exact answer but advise for you to consider. HTH Vince