Universal joint problem

[bigpaul]

I have a 71 swb 2wd. I put a 4l80e transmission in that necessitated shortening the drive line. Also had to buy a new slip yoke for the trans. When I started putting in the new drive shaft, I discovered that rear U joint (new) would move side to side about an 1/8 of an inch. I thought it was supposed to fit snugly between the tabs on the pinion yoke. Went back to the drive line shop and they produced my old u joint which was the same size as the new one.
All believed the yoke must be worn, since it wasn't present to defend itself. Back at home examined the pinion yoke and the tabs all have square corners, which to me indicates no ware (wear?). Could the ears of the yoke spread? any thoughts would be helpful