When a car owner is totally unfamiliar with the basics of the internal combustion engine it is not worthwhile for service providers to educate them and then explain the situation to their satisfaction. At this point the OP cannot post whether the “missfire” situation compression, fuel or spark related but they need help. What are the chances ms.b_blessed could post whether the problem is spark, fuel or compression?
The fall back answer remains, car owners must find an honest and reliable mechanic that they feel comfortable dealing with relative to their knowledge. At this point my best suggestion is to search out an independent shop that looks promising and take the SUV there for a second opinion. Good luck.