I recently purchased this plane:

http://hobbyking.com/hobbyking/store...m_EPS_Foam_kit

I installed the following Motor and ESC for it:

http://hobbyking.com/hobbyking/store...idProduct=6678 (the XL motor I used for this plane)

http://hobbyking.com/hobbyking/store...idProduct=3727

As I fly it, no more than couple minutes the plane started to lose power. I look at the motor, ESC, and 6S 4000 mAH Lipo that I used was hot. What happened? If these aren't really the right motor/ESC combo for it, then what motor and ESC is perfect or should I use for it?

No idea but its entirely possible you got a bad motor. Hope you broke the fan in first too

Oh yeah, I forgot to mention that I was using the stock ducted fan that came with the plane. Yeah, I did broken in the fan and still don't know what happened.

Maybe not enough cooling?

Nothing unusual "happened".

Your pushing more than the recommended power through the EDF, and the battery is dumping current to keep up with the demand.

You'll either need to step down the voltage by using a lower voltage LiPo pack, to get more time, but this will greatly decrease speed...

Or you'll need to increase the battery pack capacity.

I have a similiar setup on another plane where I use 5000mAh packs, and I get at most 3-4 minutes of flight time before I need to start bringing the plane in for a landing.

EDF's consume gobs of power...

Did you put a watt meter on your system?

Assuming your pushing 60-80A your only talking about 3-4 minutes TOPS at high draw, given the batteries you are using!

opjose is right, would look like you are drawing too much amps from your packs...rarely should they be HOT after a couple of minutes. Would recommend putting an wattmeter against the setup and see how many Amps you are drawing. Of course, the main problem could be a dodgy motor causing this, but it would be a way of finding out.....