I just posted a thread about if my horse was a buckskin or dun too and got a lot of valuable information from people replies. If you want to check it out, search "What color is my horse?" by stingerscricket. Also, do you have any pictures from the back side of your horse with the dorsal stripe? It may just be countershading, which is very common in buckskins, but its impossible to know without a picture from the back showing the stripe and tail. It is my understanding that a dorsal stripe MUST be present for it to be carrying a dun gene, but not necesarily the other dun traits, so the QH gelding would not be a dun.
"Don't flatter yourself cowboy..I was lookin at your horse."