Chiapas is interesting, but with only a couple of days it may be rushed - roads are windy and it takes time to get from A to B. If you fly into TGZ, I'd continue straight to San Cristobal de las Casas (nice town to spend some time in - visit San Juan Chamula, unique experience), San Cristobal to Palenque by way of Agua Azul takes 5 hours for 200km...
If you're set on Palenque, on short time it'd be easier as an in and out from Villahermosa (VSA). Other options are JDiver's suggestion of visiting Merida coupled with Uxmal and Campeche (Mexico's version of Cartagena), for example, or to spend some more time in Mexico City with a trip to Teotihuacan.