Have you tried cleaning the Throttle Body and or Mass Air Flow Sensor? Maybe you did and I missed it lol...

 

I forgot to mention but yes, I replaced the MAF sensor and I used a whole can of throttle body cleaner doing the throttle body and intake when I had it apart

 

Hmmm... I am at a loss on ideas beyond everything you have already tried... I hope others on the Forum will jump in and help figure it out soon... Keep us posted, I am curious as heck over your problem, hang in there

 

I sure hope you're able to find the problem. This was happening to me a few years back when I was first working on my Jimmy. I have the engine out now and am rebuilding it so I know it's fine mechanically. Have you done a compression test yet? When I pulled the motor I found cylinder 1 had low compression (about 73psi), the minimum is 100psi and should be within 70% of the max compression reading. I think the max was 140 something. I reconditioned the valves with some valve grinding compound and am going to replace the timing chain, it has a little slack, not a lot though even with over 300,000km. I pray this fixes it. If not, I only have the O2 sensors and PCU to test. I have replaced everything else (spider, crank sensor, distributor, plugs, wires, coil, ignition module thing.)

 

this thread is a touch old but

2 things, Replaced the upper intake gaskets?
No leaks from the lower intake gaskets? Air and/or coolant?
Check fuel pump voltage at connector and then at frame, when the pump prime is being ran. on my Rig the ignition switch was the catchall for this issue.

 

something else to check, put a fuel pressure gauge on it.. make sure you get 60psi when you turn the key on, and that it holds 60psi once the pump turns off. if it bleeds down fast enough to notice it, there's a a good chance your CPI unit is leaking internally.

also something I've noticed no one has touched on.. might be a good time to do a leak-down test on all 6 cylinders. .it could be something like a sticky valve causing the issue.