What could be happening?

Are you replacing parts at random in hopes it will start? I think you need to have a mechanic look at it.

If you have spark and fuel but it still won't run you need to do a compression test. If all cylinders test very low or zero the timing chain has jumped. Hope that helps! Jim

A mechanic I AM A MECHANIC, WHAT CUZ IM A FEMALE I suppose idk what I'm doing right... anyway I have done compression It always reads a misfire on #4 piston...that finally went away after I cleaned the heads and changed those gaskets...yet now it'll turn over but not start!

What kinds of compression readings are you seeing? Did you double check the ignition timing? I believe on these you can still use a timing light while cranking. There's no "sawtooth" to check the ignition timing but I believe there's a mark on the vibration damper and a single arrow or something like that for you to reference the ignition timing as the engine is cranking. Hope that helps! Jim

Now my reader is stating TPS sensor circuit A says low input???

Another thing that comes to mind is the engine will not run if the cover on the throttle body assembly is not on. A friend had a 2000 Blazer and we found that out after we did a tune up on it. Hope that helps! Jim