A855 - 5 Speed

E Body pal of mine has A855-5. Returned twice for issues, once jumping out of first on decelerations. Trans came through crate in transit on one occasion.
Has 12k miles on it - in a truck shipped back and forth across the Country.

How long will it take to put 500 miles of light in town driving for break in. Wow. Replaced my TKO 5 Keisler Tremec due to leaks and 2-3 high rpm shift issues. I gave it away. Got an SST TKO 5. Taller top gear too. Put it in and drive it. Over 5k miles now. Got it quick. Perfect.