Wants to star but wont and it feels like there is back pressure almost and it may have a bad coil pack

if it has injectors first stop ,check fuel pump pressure and filters

Check all the fuses in the fuse box first

p0306?
misfire means, low combustion energy on #6

1. bad spark,
2. bad injection,
3. bad compression

there are tests for each one.

i always check compression first. that why i dont spend a fortune
guessing. 30min.,labor , done wide open throttle, 150psi min.

i also heck the fuel pressure doing the SOP leak down test. (fSm)
then the injector balance test at same time.
finds leaking injector and clogged.
got cops?
you could have swapped coil packs COPs to see if that cured mifire.
swap any other with #6
if problem follows the coil pack COPS, then its bad.
my v6 had a 3 coil pack and cant swap just one coil. all 3 or none.

the misfire is real. you can feel it and the PCM measures it.

I, feel sorry for you, after reading your problem, but don't worry you visit the
Reliable-Store they will help you for sure.
KIA Sorento V6 3 5L 2005 OEM Factory SHOP Service repair manual Download...

crank position sensor is bad

You have three choices. First, check the spark and coil system to ensure you are getting a spark. Pull off a plug wire from the coil pack and crank. Have someone watch to see sparks snapping off the coil pack. If you don't have any replace the control module under the coil packs.

Second, you may not be getting enough fuel pressure. Put a gauge on the fuel pressure test port. You may have a bad oil pressure sensor, located down above the oil filter. Check that oil pressure sender and make sure the connector is pushed in. The power to the fuel pump runs through the oil sender. If the engine starts and oil pressure doesn't come up quickly, the computer will shut off the fuel pump. Check this and you can also manually engage the fuel pump from the relay block down by the passenger feet.

Third choice, and it's a long shot, check the harmonic balancer and the crank position sensor. If the sensor is bad, the computer has no idea when to fire the spark plugs. A magnet is on the harmonic balancer and flys by a sensor to induce a voltage in the coil and tell the computer what position the crank is in.

You also may have a bad computer.

You can figure it out.

Maybe the fuel pump is going out have the fuel pressure checked. Or you have a defective coil pack. You should have taken it back to who ever put the coil pack on, right away when you first started having trouble.

most likely the coil packs are shorted or bad

The other coil pack replacement would not be a bad idea. The rubber around the coil pack that is worn could be letting in moisture and condensation, thus cutting out .

Another possibility is the fuel system is loosing pressure and cutting out. The fuel pump and fuel pump sender could be the problem

Good Luck

have you ck=hecked the crankshaft posisition sensor.if its bad the coil pack wont fire.