When they come back from stealing horses in Mexico, Gus says they have "over 100 horses, and 2 lost Irishmen". When the horses are standing in the river, there are only about 60 horses in the herd, not over 100.
During the night time raid for horses to Mexico, when they show the moon, it is barely a sliver, so the night would be very dark. When they show Gus and the boys, there are very bright lights in the background lighting their faces. Obviously stage lighting is used so you can see the characters faces.
When Call is breaking the "hell bitch", and he walks up with the saddle, the horse is mostly white with a black spot on its neck. After the horse bucks and Call drops the saddle, the horse has a lot more grey in its coat, and the spot on its neck is gone.
Before leaving Lonesome Dove when Gus and Lorena are "Cutting the cards", the fifty dollars keeps changing positions on the table.
After Jake gets to Lonesome Dove, and he and Gus are sitting and talking, as Jake is falling asleep, Gus sets the Jug down, and when the camera angle changes, he sets it down again.
In real life, the first Texas-to-Montana cattle drive actually took place in 1866, at least 10 years before the McCrae-Call drive, although the characters may not have not have known this.
The "Hell Bitch" is described as a "Kiowa mare," but is plainly a gelding.
When Captain Call is breaking the "hell bitch" you can see clearly a flank strap which makes the horse buck.
When the storm is first seen appearing on the horizon, the storm is obviously a projection on a screen (identifiable by the fact that all the bushes on the ground are holding perfectly still and no dust is being kicked up.)
During the scene where Captain Call is aboard the bucking
"hell bitch" and the two come out of the round pen and head off through the yard past the house, it is easy to see that Call is falling off before the camera switches.
Bol is ringing the dinner bell. As Gus and the others are heading into the cabin, Gus repeats "We hear you" and goes in. As we hear him say it the last time, the camera changes to inside the cabin and we hear the rest of what Gus says, but his lips aren't moving.