I can't tell if it's me doing something weird or if I just need a different saddle? Whenever I try to hustle my horse in between the barrels, I lean forward and when I try to kick I like propel my whole body forward like I'm trying to stand up if that makes sense? It's like I'm posting kinda, instead of just leaning the upper body and kicking but staying still in the saddle. The brand I have is a diamond cross.  Edit: I have only ran in a few different brands and I seem to do it in all, so it must be me? My saddle is not too small, if anything it may be a bit big. 

Try letting the stirrups out. 
Are you feet getting behind you?

Like riding without stirrups? And yeah I have a tendency to let my legs get behind me. It's typically only when I'm running like the situation above. When I ride slow I usually do a good job not letting them get behind me.

If you're legs are getting behind you, it's the saddle. It could be the way the stirrups or hung, or the saddle could be too small for you.

Yeah I think I do possibly need more forward hung stirrups. I don't think my saddle would be too small though, but I guess I'm not sure. It's a 15 inch and I'm not very big around but I am tall and have long legs.

I douby that you can make a saddle have forward hung stirrups if it did not come that way.  I bought a Josey saddle that does have the forward hung stirrups. Seriously, I kept falling off the side.  I kept thinking that I may be old but darn I can ride better than this.  I wasn't about to get rid of the sadde because it wasnt cheap.  I had to move the stirrups up and down until i found the "sweet" spot.  It took about 6 months of experimenting!!  There is a learning curve on those forward hung stirrups.  I love my saddle now.