I built a sliding gate

Last year I built a large sliding gate to get a car through, something that's common in this area, although it seems nobody really knows how they should be built, they just copy existing gates. It slides across a header beam on a rail.

Photos here: https://www.icloud.com/sharedalbum/#...D-419DEE3CF777

So anyways, I installed 2 2x8s as the header beam all the way across, which is the biggest size I've seen anybody use. I used lag bolts to attach them to the 6x6 posts, but the hardware guy said I could just use these thick 2 inch screws (or bolts, I forget what they're called, but they're sharp) to attach the rail to the header. In retrospect this meant that only a tiny amount of each screw was actually going into the 2nd 2x8.

This spring I noticed that the two header boards were not really joined properly, there was a gap between them in some spots, so it wasn't quite clear to me if the gate was mainly just hanging off the front board. So I lagged them together using a couple of lag bolts in the middle of each span, top and bottom. Is that adequate? The spans are 11 ft each.

More concerning, the corner of the gate had sagged downwards a bit. On closer inspection the header boards had cracked and had sagged forward a bit at the top. One potential issue is that the the post had been a bit short on that side, so when I lagged the header to it, I did so in the middle of the header boards, rather than at the top. I don't know if that allowed the top of the board to pull forward and crack, or what.

Do you have any ideas for how to fix this problem, or how concerned I should be about those cracks? The crack on the back runs the whole length of the header. The one on the front is covered by the rail but from what I can see I think it stops after a bit.

Thanks in advance for your help