Has a 6.0 L with bad misfire under a load and is

Question edited for clarity. Full year make model in title and mis-spelling of 'misfire'.
Question moved to sub category.

The misfire code only tell you that, unfortunately it doesn't tell you why. When swapping parts to test theories, only swap one thing, one cylinder to one cylinder and only one item, the coil, the plug or the wires, not all three. What was the make of the Crankshaft Sensor? Only buy quality OEM replacements as there is a history of bad ones from Mexico and China.

Wouldn't hurt to check the wires again. This has a neat diagram.

https://www.silveradosierra.com/threads/5-3-firing-order-cylinder-diagram.734633/

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It's not the transmission , you have an engine misfire ! Have you taken to a shop that has a scan tool that shows misfire counter ? Misfire Testing with Scan Tool Tip Clip

No a knock sensor can not make a misfire. Check the coils, plugs and fuel pressure .The random misfires are cause the knock sensor to throw the code.

Don't need codes to have any number of problems

No misfire will ever be the same on your ford

Some coils set PO300 Codes,some show up on
a scan tool in Mode $06 under cyl misfires & some
coils you just have to walk a new one.

On a 2006 ALL the coils are bad by now, as well as the
front O2 Sensors

Change the Plugs every 3 years or every 2 on a 3 valve 5.4
or they will get stuck in there

Use the champion ones #7989

This sounds more like a misfire under load than a transmission issue. This is one of the most misdiagnosed problems we see on a regular basis. The fact that it is only noticeable while going up an incline leads me to believe you likely have worn out spark plugs, and/or a weak ignition coil.
While you do not have a check engine light on, this can happen when you have only a minor or very intermittent misfire. Once the misfire becomes worse or happens more often, the computer will turn on the light- or cause the light to flash indicating a serious misfire which could cause catalytic converter damage.
Try having your garage monitor their scan tool data for real time misfires while driving it under a load such as the incline you mentioned, or even while brake-torquing the engine (pushing the throttle slightly while the transmission is in gear and the wheels are chocked and brakes applies) This can help duplicate the conditions where you noticed the issue. Monitoring the misfire data can help them pinpoint which cylinder(s) is misfiring and swapping spark plugs or ignition coils between cylinders can determine which component is causing the issue.

The SES light flashing means the engine management software has detected a misfire condition resulting in exceeding 3 times the federal limit of emissions. Under heavy load such as acceleration one or more cylinders are misfiring and once cruising speed is reached the engine is under a lighter load (10 to 20 percent ) that is why it stops flashing several causes of misfires are worn spark plugs ,spark plug wires, faulty ignition coil or coils fuel injector or fuel pressure problems a quick check of the computer to retrieve trouble codes should identify the problem cylinder or cylinders and will direct you in the right direction to find the faulty component but will not tell you exactly what is wrong certain test must be performed to isolate the cause.

you could have a bad injector at that cylinder or a bad coil that runs that cylinder. If I remember there is 1 coil for each cylinder. How do you know which bank is miss firing without a code set?

You could have a faulty Fuel injector problem with your poppet valve. There common to go bad and start to leak causing misfires and ruff idle. There is an upgrade to the CSFI to covert to MFI system.

Here is a link that should help you with your P0304: http://members.shaw.ca/betterthanyoutoo/Sticking%20Poppet.htm

Good luck and thank you for using fixya

check for codes, p0300 is multiple cylinder misfire, p0301-p0304 is for cylinder 1 through 4, could be bad plug or coil, try switching and see if problem moves to different cylinder

you have to read out the codes. po300 is misfire detected. maybe a coil or injector. could also be intake leak