is the circlip still on the end of the axle you took out of the new tranny? It could be possible when you pulled the axle (from the new tranny) that the circlip came off inside the diff, so your other axle is hitting it when being inserted into the tranny. See if the clip is still on the old axle. Measure the length (of the part that goes into the tranny) and number of splines on both axles to make sure they are the same.
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