need help asap starting problem

ok i wont act like a gm tech cuz im not one by any means im just a grarage mechanic but i know a little. heres my trouble i have a 97 chevy blazer with a 4.3 little over 239k auto matic 4 door now the truck has a new fuel pump and new fuel filter. heres where the odd stuff happens if the truck is started up daily and ran it runs fine and starts fine every time. however if its left siting more then a day i will not start a guy showed me some odd ball trick to get it started he did when he had the same problem in a s10 but he didnt know what made it happen or even why his trick worked. you can spray starting fluid in and it wont start the only way i have found to get it started is take off the air intake tube and manualy choke the truck while someone truns it over so a friend get in and turns the key while i have to place my hand over the intake port and after about 1 or 2 mins of it spinin over with my hand covering it kinda playing lettting it have a little air here and there it willl fire up and run let it idle for about 5 mins you can shut it down and it will start fine again till you let it sit another day or two. and there is no lights coming on on the dash or codes flashing. one guy has said it could be the computer witch is on this truck under the hood above the fender if this is the case ok dosent make sence to me that it only happens when it sits but if i go get another computer for it or vcm i was told is the right name dose it have to be flashed ot anything done or can i just plug it in and go?

also we have checked to make sure the fuel pressure was correct from the pump and it is

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 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 pressure.
Cold start should be 64-65 lbs of 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 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.