1995 Chevy Blazer 1995 Blazer stalls out after 20 minutes o

Yes it sounds like you have a crank position sensor problem, It will need to be replaced

It monitors the crankshaft and tells the computer what position, it is in to help keep the timing on track, after the computer acknowledges, where the crankshaft is it then sends the spark timing to the coil, what usually happens is, when the crank sensor becomes faulty, as it heats up it will cause an open circuit and stop sending those signals to the computer, when this happens, the computer shuts down the operation of the engine, in fear that, damage will occur if it doesnt, (basically). And this is textbook, Its just that there were other things that can cause similar symptoms, that we should've checked, the crank sensor will be located, near the crankshaft pulley usually in the upper left corner right behind it.

It can be pretty, tedious to replace, depending on what is in the way, I personally never did one on your vehicle, but I can also say, it would probably cost approx. 140 to 200 dollars to replace, part included