Tire psi and new rubber. Brand spanking new tires have those little tits on them and add to that over inflated or max psi and you are rolling on marbles. Odds are you will never have it again as you have some miles on the tires but I would lower the psi to around 30ish just to be safe.
I put a set of Nittos terra grapplers on my 06 Cummins and on the way home from tire shop I just about lost it for the same reason. I was going about 70 and merged lanes and it took off wallering all over the road like a boat. Pucker factor of 9. Got home let some air out and still felt little loose but got much better after about 200 miles.