First thing we always advise is to have your unit weighed, ideally each wheel position. Second best is weighing front and rear axle, then adjust your tire pressure according your weight and the tire manufacturer's recommendation. Each axle should be carrying the same percentage of rated capacity. For example if your front axle capacity is 10,000 and the weight slip shows 9,000 pounds, that axle is carrying 90% of its rated load. Assume your rear axle is rated 20,000 pounds, it should be carrying 90% of its capacity or 18,000 pounds.
If your weight distribution is nominal, tires inflated properly and you still have handling issues, it's time to have the chassis looked over to rule out the possibility of a suspension problem. If your chassis gets a good health report, then you can investigate aftermarket products.
Henderson's Lineup and/or 3Ts can provide good advice.
Addendum: If your Vista has a long overhang past the rear axle, that will cause the "tail wagging the dog" situation. A long wheelbase and short overhang past the rear axle (like most diesel pushers) provides the best driving experience.
