3 days outside of paris with a rental car (MSM and Loire Valley)

According to via Michelin it will take almost 5 hours to get to Chambord. I think that's optimistic, since you'll likely need to stop at least once for a break and lunch. And it's another hour between Chenonceau and Chambord. You could probably do it as long as you didn't linger over lunch or too long at Chambord.

Amboise might be a good place for the night. It's only about 15-20 minutes from Chenonceau. The next morning you could either see Chenonceau if you didn't have time on Sunday, or you could see the Chateau and Clos Luce in Amboise before heading back to Paris.

You might also consider dropping the car in St Pierre des Corps (near Tours) and taking the TGV back to Paris.

Whether or not you add another night in the Loire depends on how much you love chateaux and gardens. We plan on spending 3 nights there and see at least 6 of them.

Fougeres is enroute from MSM and makes a nice lunch break, but if you are in a rush to see Chambord and Chenonceau then you want to be past Fougeres by lunchtime and you don't really have time to stop and smell the countryside.

BTW I don't think it will take you 5 hours to get to Chambord (more like 4 not including a stop to eat), though you could see it on the way back to Paris.

If you are coming from Paris on day 1 then I wouldn't schlep out to deGaulle just to pick up a car. You could take the TGV to Rennes and get your car there.

We are landing at cDG and immediately grabbing a car and driving out of paris

brie,

For driving in France, it's advisable for each driver listed on the rental form to have either an International Driver's Permit, which is used in conjunction with your home D.L. OR a certified translation of the terms of your license in French.

Are you really set on visiting the eastern side of the Loire Valley? Because the chateaux at the western end are much closer to Mont St Michel. You could go by way of Rennes & Angers to Saumur (good place to stop for lunch) and visit Fontevraud Abbey, the Fortess of Chinon, the Chateau of Azay-le-Rideau and/or the Chateau of Villandry, for example. The western side is less touristy because day trips from Paris focus on the "big three C's" at the eastern end.

Either way, I agree with the earlier comment that you'd want to be well beyond Fougeres by lunchtime. If you drive by way of LeMans, be aware that the A28 and the A11 run together for a few miles and the signage might give the impression you've inadvertently gotten on the wrong highway, so don't panic. The southbound A28 (toward Tours) is signed direction Bordeaux, if I remember correctly. Also, about halfway between LeMans and Tours there's a town called Chateau-du-Loir. Don't let that fool you into thinking it's your exit for the chateaux of the Loire region -- it's not.

Day 1 sounds brutal to me. You will fly in, customs, bags, navigate Cdg, drive around Paris, then another 4 hours worth of driving. Deal with MSM crowds. Pacing is personal preference, but I don't like to drive more than an hour on my arrival day from the USA.