Getting right to the point, technically it isn't g+k it's like doing an air grab (Press x slightly before z) you're suppose to press the guard a little before the kick, doing this with, Tong, Tengoryu karate, Agent, Azteca and so on will seem so easy you'll just facepalm and short after you will never fail. P.S somewhat of an extra note, look at your screens zoom in to know when to do the juggle, if you do this alittle to fast with say Hunter you'll never mistakingly do the PPPP P PK or KKP P PK again. Have a good day and I hope this helped in the slightest.
I'm sure most people on the forums either don't have difficulties with this or already knew about this trick. Regardless, it does help.