CAT C15 /6NZ trouble continues

I appreciate your help. But my question is why can I merge onto a 65 mph highway full throttle, 140,000 lbs gross and all is well. And never have I had an issue pulling from a dead stop, through 10 of 18 gears, and then, as prolonged periods occur before grabbing next gear as it pulls to higher RPM , only then it starts.
And at 48 mph with foot mildly on accelerator it starts chugging, like I'm on and off the throttle 5x per second, not violently bad but it's there.
I understand what your saying about bad sealing of injectors, but why can I pull hard/ heavy for 2 to 3 minutes and all is well.
It seams like once I'm up to speed (65mph) , back our of it for 5 seconds and back on it, wow, it's nasty bad.
Yet if it's acting up and my foot is off throttle for 5+ seconds( rolling down a grade) and put foot to floor again, she'll pull the stink off a turd she pulls so good. I vision it unlike it actually is, like I'm running out of fuel and backing completely off throttle for 5+ seconds fills it back up, weird.
If I didn't know I've already got a new fuel pump, I'd point at it saying there's a pump flow issue.
Does anyone know of pump issues, new or otherwise ?

 

I just posted a reply to you but don't see it. I signed it but where did it go?
I'm pooped. Off to bed.
Quickly, it basically said how I appreciate your help but I'm kind of confused.
Loaded with 140000 pounds I can merge onto a highway foot to the floor and it pulls great provided I stay on the throttle.
From a dead standstill I've never had any issues going through the first 10 of 18 gears, but once the time is prolonged between shifting gears as my RPMs climb to pull that kind of weight that's when it all starts.
If it's stuttering going down the highway and I take my foot off the throttle to go down a mild grade and then put my foot back into it again after a 5 Second rest it pulls absolutely fantastic.
If I'm going down the highway at 65 miles an hour and for a second or two I take my foot off the throttle and then get back into it again then it starts shaking and shuddering like it's running out of fuel.
If I didn't already put a new fuel pump in well over a year ago trying to rectify this problem I'd say there was a problem with the fuel pump.
Does anybody know of any issues with cat fuel pumps?
If I had problems with the injector seats would I not have problems across the board with what I previously noted that I do without issues?
Thanks again for your continued help and I look forward to any support you or anybody else can give me.
I'm off to bed have a good night

 

Thanks for all the help and thoughts guys.
To answer all questions, and knowing some of y'all haven't read the entire post since it 1st started ( and I probably won't be reading it either, it's lonģ, complicated and turned into a novel)
The ECM has been swapped out 2 X
Once with a used ECM ( thanks to a mobile tech, once a 22 year CAT mechanic who tried diligently to resolve my issue) and a 2nd time by CAT, a brand new ECM I tried for 3+ weeks. No resolution.
Injector seals replaced 3x and examined in depth on injector extraction. I don't know what CAT found if anything when they put 6 new injectors in under warranty, but no reference was made to seals or other issues when I asked them if any signs existed pointing to blow by on any injector.
Test after elaborate test performed on contaminated fuel flow ( air in fuel) both pre and post head, 2 sight glasses tied off on passenger mirror to monitor as I drove ( tech in pass seat, district manager in bunk) pulling 139,880 Lbs up a huge grade +++ a bunch of miles. No air bubbles at all, but did stumble in their presence.

 

Thanks Dino Soar for your help.
Over the past , now quickly approaching 24 months, here's some of the items I've replaced. Ive often wondered if I'm missing something though. If anyone knows of something being missed, please, kick my butt and tell me.
Here's the list of parts changed etc;
-Injector wiring harness
-engine side, wiring harness
-throttle position sensor
-fuel pressure regulator valve
-fuel temp sensor
- air intake sensor
-boost sensor
-crank sensor
-cam sensor
- atmospheric pressure sensor
-fuel supply lines (from both tanks etc)
-fuel pump
-fuel divider valve
-fuel divertor valve
-primary fuel filter housing
-added a secondary fuel pump
"AIR DOG , Fuel / Air seperator system.
-disconnected Air Dog.
-Fuel tanks dropped to check suction tubes/ pick-up tubes
-Exhaust system dis-assembled to check for plugging.
-CAT installed a new ECM, about 3 weeks thereafter it was removed as it made zero change.
- Air to air pressure tested many times
- fuel pre & post head checked under load for any sort of air etc.
-CAT installed 6 new injectors (warranťy)
●I think I'm missing at least 1 if not 2 more sensors or other which I changed but can't currently think of ●

 

Hey guys.
I'm reworking on the truck, trying to figure out my problem once again.
Schematics indicate 3 positive and 3 negative power supplies to the ECM.
One set ( pos and neg) are connected at battery. 2nd set is also at batterys .
3rd set shows ( basically states but doesn't show) the power wire being connected at ignition circuit.
Is the actually connection at the ignition switch? Or is the actual connection made on a ignition circuit elsewhere?
With thanks. !!