Can you feel the tight spot with the center link disconnected from the Pitman arm? It should be very slight, but noticeable. If not, I suggest that your box isn't adjusted properly. Getting all the end play out of the box is critical as well, I wound up using a dial indicator to check it as the feeler gauge method didn't seem to come out right. The book doesn't really mention it, but I feel it is important to back off the top adjustment (or just remove the top) while setting the end float. Then afterwards, of course, set it back so you can just feel the tight spot.
Note that it is normal (design feature) to have some small play when the steering is off-center. While driving, the camber in the front suspension will take up the play.
Otherwise it's just a matter of examining every point and finding where the play creeps in. I went through a similar exercise a few months back, and discovered that the new peg had worked loose in the rocker arm. I must not have got it mounted properly or something. I also had a hard time getting the steering wheel locked tightly to the shaft; had to add a flat washer under the nut and I suspect it is working its way loose again.
FWIW, I got mad at the original silentblocs long ago, as they never seemed to last more than a few years (probably due to poor quality replacement parts). Replaced them with brass bushings and SS pins from BFE. The Delrin ones from TRF (and ARE) are probably just as good but I haven't worn out the brass ones yet. (I also added grease zerks so I could lube them from time to time.)