Did your Jimmy start using a lot of gas before it began its refusing to start symptons? If so, this could mean that the fuel injection assembly inside the intake manifold is worn out. This is a very common problem. Does your car blow out black smoke when it does try to run? This is a sign of a very rich condition, which would further support the injector problem. Also check your EGR valve. Theses vehicles have a digital EGR valve that tends to get carbon in side of it and it sticks open and will cause a bad running problem/starting problem. Check your fuel pressure to see if the injectors and fuel system is working correctly. This will help you narrow down whether it is an EGR fault or Injector fault. Also scan your computer for any codes. This can also be a big help.