Massive power loss pulling hills - Paccar MX13 455

Paccar MX 13 455

When I down shift from any of my high side gears more so when loaded at 30-44,000 lbs I get a miss fire or chugging from my motor. I lose all power climbing hills of all sizes (don’t feel it as bad on flat land) and once I’m back into 13th gear and feather the accelerator, I can feel the miss fire feeling go away.

The only code is for #4 injector. Saying it’s weak. But only had 1 hit on that code.

Dealership was not that concerned about the #4 injector.

We did swap rocker box with #3 rocker box to see if problem follows.

Did overhead adjustment.

Dealership’s like to see at least 3-4 hits on a code before checking out the problem. Is what Allstate Pertbilt told me.

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Hello I'm having the same issue ive replaces the #5 injector and did the overhead adjustment…i was wondering if you had fixed your problem if so plesase let me know. Thank


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