When I read your post the first thing that popped into my head was that you need more caster, as Bob said assuming everything is tight. I would add, your caster angle needs to be relative to the ground, not to the chassis. According to an article in R&C http://www.rodandcustommagazine.com/...ils/index.html stock caster was three to four degrees, but with big & littles a degree or two is right. More caster = more stability, but also eats into your turning radius - look at rail dragsters or a radical chopper.