Anyone have any suggestions? Something with bars that are more flared? I currently ride my mare in a Martin Stingray 9" gullet and it's become tight on her...

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You could try a Double J #10 or #11 tree. They are made for swayback  or hip high horses. Although the #11 is more rockered so may be too much. Here is a great thread that discusses it a bit more in depth. http://forums.barrelhorseworld.com/forum/forums/thread-view.asp?tid...

I agree, the Double J #10 or maybe the #11 but like she said the 11 has more rock then the 10, but they both are for horses that have more of a dip with larger shoulders. I have the #10. 

My gelding isn't wide, but has a sway backed.  I love my treeless saddle for him & I use a pad by "total saddle fit" that has pockets the lenght of the pad to put shim's in.  I build it up under my butt so the saddle doesn't crush his withers.  He seems to like it. 

I've been having this struggle myself, I have heard of the Double J #10 tree but I have yet to try one. They are pricey! So far the best fit I've had is a Bob Marshall Treeless, but I couldn't get the dang thing to not roll. so I sold it. I recently got a CJ Record Breaker and it seems to fit alright, got a custom Wade pad made in the form of a swayback pad where it is about an 1 1/2" in the middle, not sure if it's working yet.. Wade says I need to break it in. But truthfully I feel your pain and I wish you the best! 

How thick is the pad that you are using?

Thanks for the help! I'll check those Double J's out.  
I used to ride in a treeless but since I went treed I haven't been able to go back to the treeless.  I feel too restricted in the treeless... tho that would probably be the easier solution regarding my horse. ??‍??

I'm using a 1/2" 5 star... if I go thicker I get the small dry spots behind the withers.