One problem related to transmission fluid leaking has been reported for the 2017 GMC Sierra. The most recently reported issues are listed below.
This truck is a 3500 hd. I was pulling a camper on a 1100 mile trip. With 50 miles left I noticed that the truck was leaking transmission fluid from under the transmission cooler. Upon further investigation I found that the return hose from the trans cooler was positioned so the it rubbed on a frame component which caused a hole to rub in the aluminum trans coolant return line. I noticed this when the truck was parked running at a rest area for an hour but it was obviously an ongoing issue. Had I not noticed it when I did this condition could have caused catastrophic failure of the transmission. The dealer says there is no recall and it is not under warranty. I consider this to be a serious design flaw and a major safety issue. I was able to get to my delivery stop and get the line patched. It is at the dealer for repairs right now.