does anybody know the reason why my truck does this?

[blueb8llz]

when im going less than 15mph, my truck will go straight down the path, but as soon as i hit the throttle, itll veer to either the left or right. ive asked this before, but maybe some others out there know the fix for this.
BUT besides that ok, even say i cant fix that problem, another funny thing it does is, so say it veers to the right, i would turn my wheel on my controller to the left a little bit, usually this would center the truck so that i can go straight, but no, my trucks then starts veering to the left!! why in the world??
please someone have the answer to my nightmare
just to let you guys know, ive put heavier diff oil and got true tracks, stiff springs but didnt solve this issue.