Hello and welcome to the RTA forums !

For planning purposes we think of a full days driving of 550-600 miles to be equal to 9-10 hours of travel time with appropriate rest stops, to fill with gas, eat and cater for construction and congestion delays, but with no sight seeing. Therefor your drives are perfectly reasonable but will take longer than you are expecting, mapping programs are always over optimistic as they don't account for 'real world driving' conditions. I also usually allow a little extra time for unexpected stops/treats along the way and city congestion either end of a days drive and would 'budget' for 8.5 hours [and up to 9 hours] for the journey from Dallas to New Orleans from 'door to door'.