[MaSnaka]

It could be the steering shaft assembly is expanding in length when it get heated up from the headers causing it to bind. Just touch it after you have been driving awhile...it's hot. When it's hot or atleast still real warm loosen a set screw/nut and let the shaft find it's own comfort zone. The hotter the better. Retighten while hot and see if this helps. I did have a similar issue. Good luck
John