basically, when you create the slider post, you don’t give it the gallery format.
You click Add media above the content editor, Then select Create Galllery in the top left of the window that opens
Then after selecting all the images, you select Create Gallery at the bottom right.
Then in the new page you select Insert Gallery at the bottom right so that it inserts the gallery shortcode in the content of your slider post.
You slider post content should only have that shortcode as weaver explained