You should be fine. 5er is rated for a 1/2t although I think a 1/2t would be maxed out. It's usually the payload capacity on the 1/2t that is the limiting factor and with a 3/4t you should have a nice stable ride. Your gasser will mean a little slower acceleration and uphill power but your retired so no hurry, right. We hav ethe same trailer and 3/4t but with a diesel and we really don't notice the trailer is back there.
Bruce & Lori, now happily retired and Charli (our 60lb lap dog)
2011 F350 KR 6.7PSD, 4x4, CC, SB, Reese Elite 18k.
2015 Mountaineer 331RLT, 5thAirborne Sidewinder, Dual A/C, Fireplace, HT Seating, Dual Pane Windows, Cocoa interior.