98 Silverado 5.0 Vortec, loss of power under a load

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WB23

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Hello, I'm sure this has been discussed before. I have a 98 Silverado, 5.0 vortec.
I have a cough/shutter when under a load, like passing on the freeway. I have noticed its between about 70-78 MPH, or around 2000 RPM, also it does not do it untill after it warms up. Other than that, she runs great! Can barely even feel her running at a light.
But this has been haunting me for a while now. I pretty much have changed out every sensor under the hood, egr valve,, plugs, wires, cap, rotor, distributor, fuel pump, spider injection, coil, ICM, and still can't find it. Even had a dealership look at it to no avail. Any help is greatly appreciated!
 

L31MaxExpress

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When was the fuel filter last changed? Do not see that mentioned.

I had a coil cause my L31 in my Express van to hiccup years ago. Felt down on power and would break up under load. Insulation inside had broken down and under load it was arcing out to the metal framework that it is built around. Swapped the coil and instantly had all my missing low-end torque and my WOT passing power back. Some of the lower dollar chinesium coils are garbage.
 
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