the self centering action with the front wheels is a function of Caster.
'IF' you only added the powersteering and it drove fine before the swap then yes you have a problem with the powersteering. What it is I dunno as I've only owned one rig with powersteering and it was stock.
IF you did other mods when installing the power steering, like a new lift, then look at what changed in the caster.
Eric