Blazer runs out of gas at half tank?

try running the car without tank cap & see the results

CHECK FUEL PRESSURE COULD BE TO LOW OR PUMP JUST QUITE
SOMTIMES POUNDING UNDER CENTER OF GAS TANK WHILE CRANKING WILL GET IT STARTED AGAIN BUT THIS WILL ONLY WORK ONCE OR TWICE GET IT TO A GARAGE OR SHOP TO GET IT CHANGE IF THIS STARTS IT UP

You could try changeing the fuel filter its located under the drivers door mounted to the frame in the fuel line . But the most likely thing that it could be is the fuel pump. You could check fuse # 9 its a 20 AMP in the fuse box that feeds the relay located in the glove box but on this vehicle even if the relay wore bad the vehicle would still start it would just crank for a longer time . the fuel pump has a beck up power supply also feed from fuse #9 that runs through the oil pressure sending unit. So if its not the fuse its the pump or a bad connection at the pump and that is located inside the fuel tank witch needs to be droped to replace the fuel pumpGood luck with it but this is a common issue with blazers

Have you changed/replaced the MAF sensor?

I had one do this a few years back and when i went to replace the pump i found that there was a hose broke on the suction side og the pump about half weay up the tube whitch means i could suction gas at less then a half a tank..i found a new hose and replaced it...thats been a few years and its still running fine...btw i t ook the bed off to get at the tank its faster than droping the tank..........luck to ya .its not that bad of a fix

Usually that is a bad fuel pump. Filter is not on the tank. Test it when it doesn't start, or listen, as when you first turn the key to "run", you should hear the fuel pump cycle.

It likely needs a fuel pump, hook up a fuel pressure gauge, it needs to be 11-13 psi

The float that helps detect fuel level is most likely broken. You or a mechanic will have to remove the fuel pump from the gas tank and check and possibly replace the float. Merry Christmas.

It could be the fuel pressure regulator

I had the same problem with my blazer and it took me to completely rebuild the throttle body and put over $300 into the top end, new filter, and it still didn't stop. I finally dropped the tank and started to go through all the proper steps to remove the new fuel pump and i found that the rubber tube from the pump filter to the intake tube had a crack down the middle of it, replaced that and it ran perfectly fine. if that's not the case make certain that you didn't accidentally switch the small fuel lines like i did.(you'll notice that EVERYTHING smells like gas and you'll have fuel draining out of the charcoal cab emissions filter). hope that helps out a little bit!