Stumbling on acceleration

[ghetdjc320]

Have an interesting issue I’m trying to diagnose without firing the parts cannon at it. First off, 91 4.0 AW4. Engine is a custom built by me and I’ve build a lot of these engines. I’ve eliminated a mechanical issue and am combing through electrical. 
 

The issue first came up under spirited acceleration around 4K rpm. The speedometer was bouncing a bit (factory electric speedo) and it straight up felt like a speed limiter was hit. Almost like a fuel cut. Disconnecting the Speedo at the t case eliminated the issue interestingly enough. I swapped in a 94+ style speed sensor with the 8v reference line and it didn’t have that issue again. Not sure if it’s related but it was the first issue I had. 
 

More recently, I’ve had some stumbling under acceleration. Then it started stumbling occasionally while cruising. The stumble feels like a lack of spark and is very brief (approx 1sec). It may stumble a few times while cruising and feels like it wants to die. If i baby it along it pretty much never stumbles. Seems to get worse after driving stop and go traffic. If it’s cold, it almost never stumbles under hard acceleration. 
 

What I’ve done so far: fue pump and filter changed. Fuel pressure is holding steady. New NTK O2 sensor. New NTK CPS (zero difference between old and new CPS). 
 

I’m thinking maybe bad coil, or some distributor issues at this point. Please let me know you thoughts as if like to narrow this down a bit and get everyone’s input before I but the next part lol. 
 

Thanks on advance!

[olddude]

My truck was doing that and I thought it might be the tps, so I replaced and it was worse. Tried to adjust using cruisers method but had a hard time getting readings.

So, I put the old tps back on using the old method of matching the markings from where it was set. It's better but still stumbles after idling for a while. I have since installed a REM and it registers 13 @ idle which is low. I need to adjust it up to 18. 

[ghetdjc320]

I should note as well that I’m running an accel coil with dui cap and plug wires. 

[MiNi Beast]

O2 sensor, intake leak, and valves seats..   

[ghetdjc320]

O2 replaced with NTK oem. No difference. It’s definitely not mechanical. Either the spark or fuel is cutting momentarily