I towed my boat for the first time after adding bigger tires. Right around 70 mph something is shaking real hard. Hard enough that I wouldn’t drive over 67 mph for a 7 hour drive. The boat is about 4000 lbs. bed was full with a family of 5. Tires went from 275 55 20 to 275 65 20 A/T tires. Zero issues with the boat not attached. I went through death shake with a 3rd gen I had for years. It wasn’t that bad but it didn’t feel far off which is why I didn’t go faster than 67 - I felt safe there. That 3 mph is a world of difference. Not sure I want to deal with it again. Feeling like I just wasted 1200 on rubber. Any ideas/suggestions? Don’t want it to be another nightmare. Thanks