Check the weight on both axles. If you are way under or overweight on the steer axle, it will effect how the tires are standing upright.
If you are towing, when there is a handling problem, it can be that the weight is way to low on the steering axle.
Also what model year? E-350 or E-450 chassis?
It matters.
What are your GVWR? Front and rear axle weight ratings? If you can check the weight on each axle, it will give us a great idea of what the problem might be. If there is a recycling center, moving van company, or CAT scale nearby, they can check the weight on each axle.
Also since you are having a problem with steering, if you can check the weight of one front tire, and the total on the front axle, it will be helpful. Some RV's with a slide on the drivers side might have 2,200 pounds on the passenger side and say 2,800 pounds on the drivers side. This might overload the left side tire, while just checking the front axle weight and finding it is 5,000 pounds and acceptable, checking side to side might indicate the real problem, and that the tire is dangerous load on it.
Fred.