X2 on the alignment. Also, check the tire pressures.
Often the tires pressures are low to give a softer ride but that softer ride can contribute to sway. You can safely increase tire pressures up to what is shown on the tire sidewalls. If it doesn't help, just let the pressures back down. More often than not, sway is reduced with higher tire pressures and at zero cost.
Sherm & Terry w/rescues Steve (std Poodle) & Eydie (min Schnauzer)
2015 Jay Flight 27RLS (Camped: 102 nights 2015, 90 nights 2016)
2006 Ford F350 6.0 PSD, Lariat, 4WD, CC, LB, SRW, auto., Camper pkg.