2002 Rodeo Starts and Stalls.

Hi all, somewhat new to the forum and was wondering if someone might help. I have a 2002 Isuzu Rodeo LS, 2wd, automatic transmission, with 123K, and the V6. This thing has been running great since i got it a year or so ago. it did need an 02 sensor about 6 months ago but that's been about it.
sorry this is so long but i want to provide as much info as possible....About 1 week ago i noticed a fuel leak where the lines connect next to the transmission. i noticed on the return line that the small plastic retainer inside the line was broken, causing the flexible line to not lock onto the metal line. Went to the dealer, got the new lines and replaced them. Tried to start the truck and it starts for about 1 second and then stalls / shuts off.
so first things first.
1. I check that plastic parts that came off the old line and everything is there so i don't thing anything fell into the line
2. Checked for codes with 2 different OBD2 scanners - no codes are being set
3. i can hear the fuel pump priming and it pumps when the truck starts... for the brief second it does.
4. fuel rail stays pressurized with key off.
when i replaced the lines i took the intake off as i could not get them to disconnect behind the engine. i marked all connects and vacuum lines (which there were only a handful of).
4. replaced intake manifold gaskets - heard this was a common issue
5. pulled intake back off and checked and rechecked and re rechecked everything.
6. all plugs getting spark.
7. all injectors firing
8. swapped some vacuum lines near regulator thinking i confused them.
9. checked air cleaner
10. pulled EGR off, not too dirty at all.
11. has plenty of oil
12. has plenty of coolant
13. looked into the oil fill and cams are rotating.
14. installed new MAF
still no change; starts and then shuts off / stalls after about 1 second.
15. battery on tender, voltage ok.
16. rechecked for codes - non being stored
17. rechecked vacuum lines again

So im stumped. any suggestions? i really think its something i did when i pulled off the intake and not a coincidence. all connectors are in the right place. all vacuum lines are in the right place according to the emmisions label. what else could it be?

Ive read a few things about a fuel pump relay that needs to operate when in crank mode or after the engine starts. all relays and fuses in the engine compartment, under the dash, and in the fuse panel were tested and operate.

i dont want to start throwing parts at it. would like to diagnose the issue and fix it.

Someone please help...

thanks for reading and any help your able to provide.

-Chuck:runaround:

I was going to guess fuel pressure regulator, but you said you have good pressure, so that is probably not it ...

My Truck, same engine and same mileage, does the same thing when warm. Once mine is warm and if I shut it off and come back 15-100 minutes later it will crank and so start. Try it a second or third time it will then start ... I've had this issue for the past year and I still am not sure what the issue is ...

i wish it would, at the very least, start and stay started just for a few minutes. i had a buddy bring by a service manual and ran through a ton of diagnostic step by step procedures and everything seems to check out. i think my next step is the dealer because i think its intermittent and need a Tech II scanner to monitor everything realtime.