Need Help Please

I have a 1995 S-10 Blazer that will crank some times but sometimes won't. We have replaced the spider fuel injetor we are getting fuel but when we try to crank it it may or may not crank if we get it to crank it will run till we shut it off and it will crank the rest of that day but if we try to crank it the next day it will spin over but will not start then we will have to wait a few days to get it to start again.

When the problem occurs, have a helper crank it, while you visually check for spark at the plugs. If you have spark everywhere, use a gage and check fuel pressure. Some of the national brand auto stores used to loan out a fuel pressure gage, if you don't have one. Sometimes the fuel poppets need cleaning? Any applicable trouble codes?

As said check for spark and lose of fuel pressure.

On yours you will need around 60 lbs cold engine while cranking to start fuel pressure not just 58-59 to squirt injectors.
A quick test for fuel delivery problem is a shot of carb cleaner in intake.
If carb cleaner makes it start good then you have low fuel pressure or delivery problem.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
Until the pump gets hot and has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressures.
Cold start should be 64-65 lbs of pressure.
The 95 or yours is 55/61 lbs pressure
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 55/61 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post-back fuel pressure readings.

Remember a fuel pump pressure regulator controls the pressure and maintains a steady pressure depending on engine load and vacuum.
It has to be capable of producing higher pressure than the regulated pressure.

The fuel pressure controls pressure and can leak off or bypass pressure