The steering wheel of my 2011 Maxima SV becomes stiff intermittently while driving. Sometimes it is smooth but usually it is stiff and hard to turn. The steering pump was replaced about 6 months but didn't help much. I put in 2 bottles of Lucas power steering fix fluid, and that didn't help. When I turn the steering wheel to the end and let go, it slowly returns to the original position, so I don't think it's the pump. Any way I can diagnose he rack?