Try moving the front upper arm back (more caster). Also check your front droop, make sure it is 0 or +1. Are the front axles in the center or are you using the eccentric cups with the axles in the lower position?
You can try raising the rear upper link or moving it to the outside hole, and you should try these regardless, one at a time, but I don't think either is the solution.
What size tires are you using front and rear?