I just re read the post again and you said you changed the hpo rail also and still leaks.But you said you switched injectors #8 with #2 and the leak followed to #2 correct and this is a new injector.Where is the leak at on the injector if it's in the top around those two weep holes.then the injector is back because air is passing between the the spool valve and spool valve body "internal bleeding ".This will cause a truck to idle perfect when cold most times and as it warms up goes to missing.You will chase ghosts if you don't know what your looking for.
This is how I fined a bad injector the easy way and I'm not doing the work twice.You pressurize the system and you spray either a little power clean or bleach white around the top of the injector.If you don't have any bubbles they are good but if you have a slow bubble then that injector is bad and will leak when truck is warm.I do this after I have replaced the o rings in the system it's the last step before I put the valve covers back on.
