Car cranks but will not start

I have had two Chevrolet Blazers do the same thing, at about the same mileage that you have on your Jimmy (essentially the same vehicle). On both of mine it was the fuel pump. So start with checking the fuel pressure, as detailed in the article below.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

With the key on, but not cranking the engine, you should get at least 60 psi of fuel pressure. Any less than that is not enough to start it.

Another test that you could do (the backyard mechanic way) would be to spray some starting fluid into the intake. You would loosen the wingnut that is on top of the engine, behind where the air cleaner duct goes in. Then gently pull up and towards the front of the vehicle on the air duct. Spray the starting fluid into the throttle for about one second. Then put it back together and turn the key. If the engine fires, then you are getting sparks, but not fuel.

I personally highly suggest doing the proper fuel pressure test, as it will point directly to the problem.