Connecting thru DFW

Few more weeks & we're on our way. With airfares sky high this year, we found the best fare from Detroit to Zih was thru Dallas. As this will be our first time connecting thru Dallas, on the outbound from Detroit we arrive in Dallas at the North terminal & depart from terminal D to Zih, with a 1hr & 45min layover.
On the return from Zih, we arrive in Dallas at Terminal D & our departure to Detroit is from the North terminal. Here we have a 2 hr & 15 min layover.
Questions:
- How far is it between terminals,
- Is this enough of a layover, considering we need to go thru customs on our return, will we be strapped for time.
Any info would be much appreciated.