Engine misfiring My 2005 Ford Escape XLT is only firing on 3 of 6 cylinders. Is this a common problem with a simple solution, or a more complex one?

Yes, there is a possibility the plugs could be causing the problem. Check the spark plugs ,One at a Time, to see what the electrode end inside the engine looks like. It would be a good idea to change them anyway. There are other reasons for a misfire. I have attached a link giving a list of other causes of misfires.
https://www.arnoldclark.com/newsroom/2502-the-most-common-causes-of-engine-misfires

the car needs service, that is what the CEL lamp means. clearly.
try new spark plugs that skipping is engine misfire,
my guess, DTC error P0300, called misfire.
15 year old cars need service, for sure.
there are many cause, of stalls. and I will not list them.
A shop will do diagnosis, and use meters and such to find the true case. (lots it can be, it is not a moped is complex)

ever do the 60k mile tune up, yet (aka: tuneups?)
clean the EGR first, most cars with EGR need 50k service,
if it stick open motor will stall .
idle controls are complex on newer cars with fly by wire.
if not fly by wire, clean the ISC .
possible #3 is induction air leaks (aka vacuum leaks)
Is the CEL lamp glowing? running?
if yes, the ECU is trying its best to tell you what is wrong.
listen to it, that is called a scan tool (cheap as $7)

Gear ratio does point to an internal transmission issue. The misfires can easily be diagnosed by swapping thing around and seeing if the code follows. For example misfire in cylinder number 1 & 2 swap coils to cylinder number 3 & 4 and if the code changes from P0301(2) to P 0303(4) you know you need coils.

Your an 2005 Ford Escape 3.0L, you don`t have a distributor. Each cylinder has it`s own coil and is controlled by the PCM. You need to scan the PCM to determine which cylinder is loosing power ( misfire). P0301 cylinder #1, P0302 Cylinder #2 and so on. The coils are common problems with this vehicle, but pay close attention that the drivers in the PCM are not at fault. #1 cylinder is on passenger side near the firewall passenger compartment. firing order as follows, Bank #1 1-2-3 front of engine to rear. nearest the passenger compartment. I`m an ASE Master with 30 years experience. Be careful, don`t waste money on unneeded parts! I own my own company. 805-369-4589 Jerry Bryant. Advise is free, but like reading a diagnostic manual does not mean the problem is solved. Correct diagnoses and system inspection and testing is what needs to be done so you don`t waste money!

I am assuming that you have a V6 Engine because 1, 3 and 5 would be on the other side of 2, 4 and 6. A Striaght in line engine would have them all in a row.

But another way to locate your spark plugs would be to find your Spark plug wires and follow them to the spark plug.

Good Luck

Take the cover off the engine, there you will view below you three coils, disconnect the wire from the middle one only after disconnecting the battery, disconnect the wire harness to that coil, remove the not securing that with a 5/16 socket trhen pull straight up, replacement is opposite removal.

Cylinders 1-2-3-4 are on the passenger side. 5-6-7-8 are on the drivers side.

Check the spark output on the number 6 coil by removing it, installing a spark tester, and start the vehicle. If there is no spark swap the coil with the #5 coil. If it still doesn't spark replace the coil. Very common for them to go bad.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

If the engine has a P0305 DTC (Data Trouble Code) for a "cylinder 5 mis-fire detected", then the first thing to do is to do a compression test to determine if the mis-fire is actually being caused by a mechanical problem, or an electronic problem.

If the engine really does have low compression on the #5 cylinder then that is caused by a mechanical mis-fire and nothing electronic will repair it, and the most common causes for a mechanical mis-fire would be a burnt or bent intake or exhaust valve, a warped cylinder head or damaged head gasket, or a damaged piston. You can call around and find a repair shop that will do a "compression leak down test" if you want to know exactly what is causing the compression leak without any dis-assembly to the engine.

Swap the coil pack with another cylender. If the error code follows the coil pack then replace the coilpack.