1997 7.4l - At my wits end with an irregular miss.

All right yall, I need some help. 97 Suburban 7.4l 4l80e 4wd 185k miles. Irregular miss starts at 3k rpm and gets worse with engine speed. Load is not necessary - it will do it in neutral. No codes. Previous owner (buddy of mine) did injectors, fuel pressure regulator, plugs, wires, throttle position sensor, fuel pump. I changed coil, ignition module, distributor (found it had been replaced by the owner previous to my buddy in 2019 - had play in the shaft), ecm (I damaged the original when I opened it to inspect), MAF, O2 sensors, upper and lower intake manifold gaskets, crank position sensor, fuel pump (was a cheap universal, I installed a delphi), and replaced the catalytic converters with a universal converter. There was a lean code for a time - I found that the oring in the fp regulator had been pinched and the screen broken. I replaced the oring and screen, those codes have not come back. I think I'm remembering all the parts that have been replaced. I'm not normally the parts cannon type, but I'm at my whits end on this one.

It is making about 60# of fuel pressure. The injectors installed are the yellow ford style injectors. They do not appear to leak and the spray pattern looks ok by my eye (checked installed with the upper intake off, cranking with the coil unplugged).

I will note - sometimes you can get a clean run out of it up to 60mph without missing. It will do it after that first pull 100% of the time. The miss seems to get worse the more it happens, as though something heats up and then starts to progressively get worse.

I would love any kind of input on this. I am about to throw in the towel and drop a 5.3 in it that I have, or carb swap it, but really I got the thing to haul a camper with my family. It would be nice to get the 454 sorted and retain the factory efi. Thanks all!

I believe your fuel pressure is low. One help is a 6 foot hose on fuel pressure guage, tuck hose under wiper so it is visable while driving.
A vehicle/maint history would help. Were upgraded injectors installed? Intake Manifold gaskets? Are any misses shown on a live data scan while driving? Any out of place sensor readings on live scan?
Factory manual troubleshooting very good. The 97 is maybe 9-10 pages in, 98 is same for fuel I think.

I don't know how it is with our cars, but I've never had any problems unscrewing and reattaching drive shafts, regardless of the position. Drive shafts are usually balanced, but only internally, not in connection with the differential or the transmission where they are bolted.

It's more likely that you have a resonance problem. This means that a wheel, it's never 100% round, and even if it is balanced, it's not completely even. The larger the wheels and the heavier the rim/tire combination, the more pronounced this effect is.

There's a resonance speed for all wheel sizes. I remember this from the BMW 7 Series I used to work on a lot. The resonance speed was around 110 km/h.

Why is this important?

If you have play in axle components, you often don't even notice it. But when the wheel reaches its resonance speed, you do. Then it starts to happen that this wheel swinging, combined with the play in the axle, can lead to stronger vibrations.

You can have your wheels balanced for a long time, but it doesn't help at all. Therefore, you need to check whether your rims are bent or whether there is any play in the axles. This is sometimes not easy to determine. Because: if you shake a wheel that's been raised off the ground with a jack, you often don't notice any play there due to the limited strength of the person.

In Germany, the TÜV (safety and emissions inspection) sometimes uses so-called vibrating plates that put the wheels under real stress, and you're more likely to notice corresponding play in the axle.

If no vibrations occur with other wheels, you probably have rims that have excessive radial or lateral runout.