The statement 'the only good Indian is a dead Indian' was reportedly made by General Philip Sheridan in 1869. Washita Massacre took place in 1868.
When Sully and Mike are laying on the floor kissing at the new house, the sounds don't match what the actors are doing.
The Washita Massacre of Black Kettle's tribe by Custer happened in 1868 in Oklahoma, not in 1870s Colorado.
Cloud Dancing comes to Sully and Dr. Mike and tells them how Black Kettle and his Tribe were turned away the fort and why and where they made camp. How would he know this and so quickly? There is no way Cloud Dancing could have all that information and as soon as he does as it takes Cloud Dancing, Sully and Dr. Mike quite awhile to get to the camp on the Washita afterwards.
Custer preferred to dress in the fringed buckskins of a frontiersman when traveling out West.