I have a slight veer when I get on/off the gas--it has plagued me for years but not serious enough to replace any of my A-arm components which are the only thing I have not replaced (and which all seem tight and good, even with a bar prying on them to check for play). That said, I am running a detroit in back and tru-track in front and I am thinking when I get on/off the gas, the lockers in that situation bias power to one axle shaft which may certainly explain it.
That said, I would check both your diffs and see if you possibly have a broken axle shaft or bad diff--that would certainly have some of the symptoms you are referring to. Assuming all your suspension bushing are in OK situation, this or the a-arm is the only thing that makes sense to me. I don't see this as being a pre-load swivel issue but that is worth checking for maintenance sake.