Stephon Gilmore is an incredible talent but he isn't the shutdown corner that he used to be and the Dolphins need to challenge him.
He won't cover Tyreek Hill by himself, should Hill play and he won't likely be able to cover Jaylen Waddle alone either but the Cowboys will play safeties deep to keep the deep throws covered.
Miami isn't likely going to one-up Gilmore. He has been around way too long to be surprised anymore. He will jump routes and he will hold his coverage but the Dolphins shouldn't simply stay away from him. Making him make plays against Miami's better WRs should be the plan.
If Miami can expose Gilmore or create opportunities against him, they can keep the secondary confused and force other players to step up.
The Cowboys' secondary isn't bad but without Trevon Diggs, they are susceptible to giving up big plays. Daron Bland leads the team with 8 interceptions while Gilmore has two. Diggs is on IR and won't play. Miami will need to force the Cowboys to use their safeties over the top to cover their WRs. If they do that, the running game will be effective.
Regardless, Miami has to play Gilmore at the line. If he plays off the line, Miami has a good chance to get into their routes but he covers well. If he plays physical at the line of scrimmage, the Dolphins are going to need to motion away to get the WRs into their routes. This is important because the Cowboys have one of the best LBs in the NFL.