I drove from Miami to Orlando after my cruise to make a stop in WDW, and quite honestly I would not choose to do that again. I disembarked on a Friday but was on the road midday, well ahead of when I'd expect rush hour traffic, and the roads were already absolutely packed with cars. At multiple points other drivers deliberately prevented me from changing lanes or making turns, and there were points at which I thought I was going to be forced off the road and onto the shoulder. I was amazed that I got out of there without any damage to the rental car.
The tollway between Miami and Orlando wasn't bad in comparison, but once you reach Miami itself you should be prepared for a complete and utter nightmare. If you're from an area with dense traffic and aggressive drivers you can probably handle it, but I'm not used to that kind of thing and it was an incredibly unpleasant experience for me.