Blazer takes forever to start

Make sure the battery has a full charge.

Are you missing anything besides fuel? Engine cranking visually check for spark at the spark plugs. Also, check for fuel injector pulse. If your missing everything, check for an rpm signal.

With the spider fuel system, start-up fuel pressure can be critical, around 60--66 psi. At the fuel pump connector, engine cranking, gray wire is voltage, black is ground. If good voltage and ground with no fuel pump action, have to suspect the fuel pump.

Are you saying it cranks good but won't start? If so, have a helper crank it while you visually check for spark at the spark plugs. If spark everywhere, use a gage and check fuel pressure. Also, check for fuel injector pulse, engine cranking.

If your saying the starter won't even crank? Then make sure battery has a full charge and check wiring circuits at the starter. Any testing at the starter make sure tranny is in park or neutral and the parking brake is set.

It possibly could be the alternator.

You say it has fuel pressure, if it has sequential fuel injection it needs about 70psi to start the engine.
If it cranks and has spark to the plugs, the anti-theft system is not involved.
You did not mention the rotor, I assume you have spark to the plugs not just out of the coil.
If you have not yet checked cranking fuel pressure, I would start there. The pump could be weak or the filter stopped up.

Check the fuel pump for pressure by removing the send line from the fuel filter and ranking the car. Place the line in an empty 2 liter soda bottle and have a friend crank the engine a couple of times to see if the pump sends fuel. If not, replace the fuel pump an replace the filter since you will have a line removed already.

Try replacing the fuel filter first, but it sounds like your loosing your fuel pressure prim when the fuel pump is not working. The fuel pressure should be 62-65 PSI with the engine not running the the ignition key turned on and should drop about 5 psi when the engine is running. If you turn the engine off and check the fuel pressure, it stat steady for morn then 15min. If it drops fast, then you have a leak at your fuel pressure regulator (common) or your return fuel check valve which is located at your fuel sending unit.
Start with the simple and replace the fuel filter, it could just be to dirty to pressurize the fuel system fast enough giving you the hard start.
Thank you for using Fixya and good luck

No, the fuel pressure valve may be stuck open so that the fuel pressure is too low when you start up, but the pump keeps up after the engine starts...
The fuel pressure valve is draining the fuel back into the fuel tank when the Blazer is parked.

If your engine is cranking really strong make sure you have proper engine timing. If your engine is having a hard time cranking like its cranking really slow. You probably need to check your battery.

you have to put a guage on it to find out the pressure it may kick on but not enough pressure

It could be your fuel pressure regulator, check this link for details:

http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c1528022b9c4

That's what it looks like.