Help!!! Frankfurt, Heidelberg, Strasboug in 5 days

Fly from DFW to Frankfurt. From there I think train travel would be your best bet. German trains are very nice. I would add Colmar to your list perhaps before Strasbourg. You could even then take the train from Strasbourg to Paris and fly back from there.
We stayed at the Hotel Maison des Tetes in Colmar. Be sure to visit the Unterlinden Museum. Colmar is a quaint, picturesque little town with canals and wood-timbered houses.

It might work well to take the train from Frankfurt to Heidelberg to Stuttgart, pick up a rental car in Stuttgart, drive to Strasbourg, and drive back to Frankfurt. Here's why:

If you book NOW at www.bahn.de, you can get a Sparpreis fare as low as 19 euro for Frankfurt-Stuttgart, including a stopover in Heidelberg. Sparpreis tickets are for specific departure dates and times and are non-refundable and non-exchangeable.

Go to the site and click on the drop-down flag menu for English. Enter Frankfurt(Main) as your departure point, a departure time, and Stuttgart Hbf as your arrival point. Choose the number of passengers and then click on "Further options." On the new page enter Heidelberg in the "Via" field and select the number of hours you wish for your stopover there. Then click on "Search." You'll be given a number of departure times. In the Savings fare column click on "Check availability" for your preferred departure time or click on "Check all." Proceed with booking the time of your choice and print your own tickets.

There is no relatively direct train route from Stuttgart to Strasbourg. You would make a minimum of three connections and the trip would take around eight hours.

According to viamichelin.com, driving time would be around two hours.

"There is no relatively direct train route from Stuttgart to Strasbourg. You would make a minimum of three connections and the trip would take around eight hours."

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The TGV goes direct from Stuttgart to Strasbourg (Paris, actually) with a stop in Karlsruhe in 1h19m, and there are a number of IC/ICE/Reg connections in just under 2 hours, but yes, those require changes in Karlsruhe and Appenweier.

If you want to do it with a Baden-Württemberg-Ticket, there are regional connections via Karlsruhe and Appenweier in 2½ hrs. Now, if it were I, I would take the 3 train, 4 hour connection through the Black Forest via Freudenstadt just for the trip down the Murg river to Baden-Baden. I might also spend a few hours in Freudenstadt.

Oops! I messed this one up big time--and I just figured out why. On the bahn.de site after I had entered Heidelberg as a stopover between Frankfurt and Stuttgart, I forgot to remove it when I looked for trains from Stuttgart to Strasbourg so bahn.de gave me a route from Stuttgart to Strasbourg via Heidelberg. It didn't seem at all likely that one couldn't travel quickly from Stuttgart to Strasbourg by train so I should have questioned my own findings.

Forget what I said about renting a car. Take trains for all your routes.

"so bahn.de gave me a route from Stuttgart to Strasbourg via Heidelberg."

And you probably also had inserted a stayover of several hour, at least, in Heidelberg.

I've done that before on the Bahn website. It's a little trap that's easy to fall into. You put in a "via" and it doesn't remove it when you change destinations, but it doesn't show what you've done unless you bring up the details. I've looked up a short trip in Bavaria and wondered why it takes 11 hours, only to find I still had Hannover as a via. Something of which for everyone to take note.

Lee, It's comforting to know that I'm not the only one who has made that mistake! And, yes, I'm sure that the stopover time I had chosen for Heidelberg was still in effect.

Joe, If you book NOW at www.bahn.de, you can get Europa-Spezial Frankreich fares as low as 29 euro for Stuttgart-Strasbourg and Strasbourg-Frankfurt. Like the Sparpreis ticket I described above, these discount tickets are non-exchangeable and non-refundable so you have to be able to commit to a specific departure date and time.