Changed wires&plugs recently and think I mixed up the firing order trucks runs but very poorly

running rough? Were the plug wires serviced recently...get the firing order from your parts store, then trace each wire from spark box to cylinder...Least costly attempt...

How do you change a cylinder? That's generally a major machine-shop overhaul on non-aircraft engines, and you should have serviced rings and bearings for all of the other cylinders as well. I assume you meant you did something else on Cylinder #1. Did you mean you changed the spark plug cable, or was it the fuel injector? Note: if you mixed up spark plug cables, you will have at least two plugs firing at the wrong time. This will make the engine run poorly, if it runs at all. Look for a sticker somewhere in the engine compartment showing the firing order, and verify that each cylinder's spark plug wire is connected to the corresponding terminal on the distributor or coil pack.

You can google the engine size and "firing order" to get a drawing or photo of the firing order online.
Example - - 1990 GMC 350 firing order diagram

if its running poor or stumbling then you have some wires/plug not firing correctly, this means a bad wire/ bad plug, or you mixed a few of them up. go back over them again and make sure you have everything hook up right.

I do this for a living and have for 25+ years. To this day when I do it I have know idea how I messed them up but i do it some times. Even when I think i am doing them one at a time. Double check your firing order (see picture below). If that's not it check the Distributer cap & rotor for any cracks or flaws. Then check the plugs for being wrong or faulty such as cracks as well. that's all I can think about at this point for you unless you knocked a vacuum line off somehow and that's possible too. I hope this helps and good luck.

backfiring is not good means a valve is not operating as it should.timing is out ....either a timing belt or distributor is going bad, or plug wires are not in proper order.

FIRING ORDERS

Before carrying out extensive tests to isolate poor running problems, check connections of spark plug wires. This is especially important if plugs, wires, distributor, etc., have been disturbed recently for service. Obviously, this is not applicable to the wireless 4.7L engine.

NOTE To avoid problems, remove and tag the spark plug wires one at a time to ease reinstallation.
For vehicles with an extensive service history, keep in mind that the distributor could have been removed previously and rewired. The resultant wiring would hold the correct firing order, but could change the relative placement of the plug towers in relation to the engine. For this reason, it is very important that you label all wires before disconnecting any of them. Also, before removal, compare the current wiring with the accompanying illustrations. If the current wiring does not match, make notes in your book to reflect how your engine is wired.

Fig. 2.5L Engine Firing Order: 1-3-4-2 Distributor Rotation: Clockwise

Fig. 3.9L Engine Firing Order: 1-6-5-4-3-2 Distributor Rotation: Clockwise

Fig. 5.2L and 5.9L Engines Firing Order: 1-8-4-3-6-5-7-2 Distributor rotation: Clockwise

Fig. 4.7L Engine Firing Order: 1-8-4-3-6-5-7-2 Distributorless Ignition

Fig. 8.0L Engine Firing Order: 1-10-9-4-3-6-5-8-7-2- Distributorless Ignition
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check plugs -plug gap-vacuum leak-fuel mix-fuel pressure-timing-pcv valve-egr valve-air filter-oil sludge build up-problem in heads[valves adjustment-burnt-weak springs if only changed wires do a complete tune-up and do a compression check

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Because you didn't say which engine this link will take you to a proper site that has what you need