01 f350 shuttering
so my dad called me today and asked me what i thought was the matter with his truck. he has a 2001 f350 ex cab long bed 2wd and he sayed he was on his way home from work the other day and he started to notice a shuttering around 35 to 40 miles an hour. so i took it for a ride today and its not the tranny of the torque converter i think. he sayed that the truck tows the camper fine but they are towing the camper to florida in a month or so and he wants to know what it may be. any input would be greatly appreciated.