Lemmon Truck. What can we do ?

We purchased a 2006 Volvo Semi Truck in Oct. of 2008.We have had all kinds of problems with it since we picked it up. We have had it back to the dealer least 5 times and just recently for the 3 rd. time for the same problem. They had the truck for about 5 days. At first they said once again that they can’t find anything wrong with it. My husband had done some research and mentioned something about an EGR valve. At first they told us that it was ok and then turned around and told us that it did need replaced and likely the problem.They also said that part of the problem may be the ignition switch which they also changed. $ 1480.17 later the truck is still doing the SAME thing. We don’t have the money to keep taking it back. We have lost at least a minimum 3 weeks of revenue because of these problems they can’t seem to fix. Do we have any kind of legal right to make them fix it the right way with out charging an arm and leg? Please help