Wheel Bolts problems of the 2000 Dodge Dakota

On 06/22/01, the rear wheel of our Dodge Dakota quad cab came off the truck while towing a horse trailer. After it was towed to sunset chrystler dealership in grenada, ms, they turned in to the warranty that the truck had been wrecked and that is why the wheel came off. Since then we fixed the rear wheel by replacing the lug bolts and nuts with some that are not a Dodge product. We found out at the time that you can not order the rear lug bolts for the Dodge Dakota qeadcab. We are now having problems with the other tires on the vehicle doing the same thing. The lug bolts are coming loose and requiring tightening almost daily. A mechanic at applewhite's garage in winona, ms looked at them and said that there is a shim behind the rim on each lug bolt. We can not find anyone that knows what or why these are on the lug bolts. This is a potentially hazarradous problem.