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I imagine that if the u-bolts loosened a few turns on the nuts, the blocks had no centering pins, I could see that happening. But the blocks usually have pins locking them in place, and if u-bolts are torqued properly, the stretch on them will keep them tight forever. I work for Freightliner Trucks, and most of those trucks even come from the factory with 1", 2", 3" blocks up front!
If you don't feel comfortable doing it, then don't do it! I'm just sayin through my experience...