Chasing a misfire or stumble

Ok so I have been going over my car (96 Cobra) for 2 weeks now trying to find what is causing a misfire or stumble when put under load. Originally I thought it was ignition related and found the #8 plug wire arcing so I replaced all the wires and plugs gapped to stock. I check the fuel system and all injectors are firing, replaced the fuel filter, and I checked for vacuum leaks and there are none. I thought the cat(s) were clogged because the engine sounded like it couldn't breathe and I was partially right. I removed the stock mid pipe and cats and put on a Bassani O/R X-pipe and the car is about 75% better. So I was looking over my SCT X4 tuner today and noticed everything was within range sensor wise except the fuel pump duty cycle was at 100% at idle and when I introduced rapid medium to heavy throttle the car stumbled, but under a light steady throttle it revved perfectly. This leads me to believe the fuel pump is dying and is already maxed at idle and anything more than a light throttle makes it difficult for the fuel pump to keep up with demand.

So if you read through all of that my question is simple, those of you who have a tuner or can data log can you tell me what your fuel pump duty cycle is at idle and under load? Also at what point does it go to 100%? The car is not heavily modded, only a JLT air intake, O/R X-pipe, flowmaster catback, and the tune is setup for these mods. The tune is not the issue because I just installed the X-pipe and tune today and the car actually improved.

If it's a misfire can check the coil packs since you've already done plugs and wires

I've checked the coil packs they are within range, plus I have 2 spares in case 1 decides to go down. I tested them cold and after driving the car at operating temp and both tests came back good. I say its a misfire because that's how the ECU called it, but it gave the random misfire code. A shop looked it over and said it was bank one having the issue and instantly blamed internal engine damage, it could be internal but before I pull and engine and rebuild it I want to be sure.

If it is internal you can always Borescope it and do a leakdown etc.

I know but before I do that I want to check all external components that can cause this. Once I find the engine has an internal failure its coming out for a forged bottom end and a complete head job.

I would compression test..if that comes in not good then do a leak down.

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The wires you installed were brand new?
they are problematic, ive had issues with mine. I have a brand new set in route to my house now.

I had a set of Ford Racing wires on the car, the #8 was arcing in the hole of the cam cover so I swapped them all with new factory replacement Ford wires and plugs. The compression test revealed the engine is in good health cranking wise. Highest cylinder was 163 the lowest was 153, only 2 cylinders were below 160. Changed the fuel pump today and the car is about 85% better than what it was, I can actually drive it and apply some throttle to it, its still hesitant under heavy load. Talking with a few tuners today I classified the problem wrong, it isn't a misfire. The proper way to think of it is like its dropping cylinders from lack of fuel or a lean misfire. The ECU can compensate mostly for the problem but not fully, I was told if the fuel pump swap doesn't fix the issues then to change the injectors because they don't seem to up to the task anymore, especially when things get hot under the hood. I rechecked fuel pressure and before the pump swap I could only manage 32 at idle or during priming when Ford originally calls for 35-45 psi according to the original Ford manual for this car. Now it has proper fuel pressure things have gotten better which leaves 3 things left to cause this issue. 1. Injectors either weak or clogged 2. Fuel pressure regulator (highly doubtful) 3. Alternator going bad. Whenever I figure out what is wrong I will update even if changing injectors don't fix the issue, this way it will help someone out later on if they have the same issue.

I've heard of many guys compression testing their motors with 80 to 100k miles and the results were in the range you were in.

My car has almost 174k and I got 180 to 190 psi
Not to shabby in my book. It kinda made sense when I got the car the owner went for a ride with me. I immediately floored it and he was like holy s*** I've never done that before. So even though It was driven it was pussy footed around.

At first I thought those #'s were low but according to the math the cranking compression should be in the 160 range. I don't know if I feel good enough about the engine to boost it but for N/A purposes and driving around for a few more thousand miles its in good health. My injectors are in route but they don't fix the issue I will perform a leak down test next to determine if the engine does have a leak, leak down test is the tell all of the sealing capabilities.

*UPDATE:

Put in new injectors and a new fuel pressure regulator and the problem got better under throttle but worse at idle. Broke down brought it to Ford for diagnosing and so far they say it appears to be a bad ECU. Waiting on final confirmation on this but the tech said it doesn't seem to be firing the injectors at the right time causing a 25% correction (lean condition) on bank 1 and a 10% correction on bank 2.

Man I hate when this happens. Unfortunate it happens a lot when we throw money into a something we can never seem to find and fix 100%

Finally found the issue, I have a burned valve or broken exhaust seat. time for a complete tear down and build up of the bottom end and rebuild of the stock heads for now, later I'll be adding a set of C-heads and custom cams to match the new short block. shooting for 500hp at the crank N/A, not really concerned about driveability when its done, mostly how it will perform in its powerband when I'm done. possibly going to sleeve it to 3.7 bore on stock stroke.