I am stuck at 6 miles...

Someone asked nearly the exact same question at a Galloway seminar I attended (except it was for a slightly longer distance, 12 miles), and he suggested A) Get to the walk break sooner. If you're doing, say, a 4:1, try a 2min:30s instead, or even a 3:1. B) Slow down, especially in the first couple miles. It looks like you're just under a 10:00/mi pace; try 10:30 or 11:00 instead.

" Gellin' " was a different question, but that got asked too ... his answer was a lot stronger than mine, but let's just say I'm a total garbage can and I wouldn't eat two gels at once. It's probably not why you hit the wall, but that's some gooey mess sitting in your stomach where the blood's going instead of your legs. If you really feel like you need two on a 10-mile run, better to eat at say mile 3 and 6 with some good glugs of water. It's pretty concentrated stuff.

I've been running for years and this is my 2c:

TriAya and HelenS are right - those are great points, apart from that, you are simply not accustomed to running long distances. While I respect all those 16week programs (especially Jeff Galloways) it seems unrealistic to me that without few prior seasons of longer distances you would be comfortable doing 20k after few weeks, regardless of the nutrition. You will do it, but the body must gradually get used to this kind of effort! Few weeks is not enough. IMHO it's too much  to keep increasing the long run by 10% week after week, even with few easy weeks in between. In the beginning of the program it works, but later the added distance is simply too much. So if this is your first real running season (from your logs it seems you haven't really run that much) just slow down for now and walk more, eventually it will be more natural.

It takes between 2 and 3 hours to deplete your internal glycogen stores ....... you are not physically "bonking" in that sense.  Your muscles/joints may not be adapted to the stress of longer running, but there is really no reason you should be crashing at 5 or 6 miles unless you are going too hard at the beginning and your heart rate it way high.

Slow down, relax and don't worry about the miles or the clock, just run or run/walk as the plan you are doing calls for and you'll get through this.  It really sounds like a mental thing to me, but I'm no sports psychologist.

I tend to agree with Daremo... and when training for a half mary awhile back I also got stuck at the 6 mile mark.  I knew it wasn't nutrition/hydration, though I did try changing that up with no improvement.  I run with music and my solution was to find a "mile 6 song"... something that completely inspired me to listen to at that point in my run.  Sounds silly but it worked.