Let's make sure we are all on the same track. I have changed.
1: Every sensor is new except knock sensors, Engine temp sensor. Temp sensor is reading correct as measured with a temp gun. All sensors are reading in the normal expected range. TPS, MAF, Map, IAT, All o2 sensors, IAC seems to be working properly,
2: Timing set. The installed set was new. Changed out to a new Cloys set. Trying to make sure the first installed set was not the problem. Cam is installed dot to dot.
3: Plug wires. The first set were new AcDelco. The second set are 8.0 mm Can not remember the brand but they were not cheap.
4: 3 Sets of spark plugs. A new set, then a used set, then another new set. They are gapped to 0.045.
5: Numerous compression checks. All cylinders are 155/160. Passed leak down test.
6: New distributor.
7: 3 Caps/rotors. New, used, New with new distributor.
8: 5.O injectors less that a year old and ran perfect in old engine. Reman stock GM injectors, Tested and working as they should and do not leak down.
9: Cat's are not plugged. Tested and shows less than 1 PSI at 2K rpm.
10: New FPR and FP is at 58PSI.
11: New AcDelco fuel pump.
12: New fuel filter.
13: Stock untouched black box ECM. Tried a tuned 0411, no difference.
14: Steady vacuum needle at 19 inhg.
15: What else is left?
Nothing has changed how it runs. It should be running like a bazillion dollars but it is missing and running rough.
When cold 1 cylinder feels almost dead. It runs better when hot.
Cylinder drop test, All cylinders make a difference about the same on each one.
I don't believe the lower intake is leaking underneath. Upper intake is not leaking.
There are no vacuum leaks i can hear or find.