Did you check to see if your reservoir screen was blocked up. Your steering rack may be starved of fluid and that's why you're steering is stiff.

Also, when you changed out your steering rack, you might have inadvertently put extra tension on the steering shaft. Go under your rig and loosen the pinch bolts on both the upper and lower sections of the rag joint. Maybe you tightened up the bolts of the rag joint after you secured the rag joint halves to the steering rack and steering shaft. As you tightened the bolts that bring the two rag joints halves together, it makes the steering shaft bound up a bit because it's too tight. By loosening both pinch bolts for the rag joint halves, you will let the halves reset into a more neutral or loose state unbinding the steering shaft.