I think you may be overblowing the number of built trans with this problem and misleading and scaring the OP. While the people you know may have issues, that doesn't represent the average. Both Mike and Even build transmissions that rarely have issues.Sounds like you have the same downshift jerking problem that half the people with built trans I know have. Mine does it bad and has been doing it for over 100,000 miles of 550-650 hp. I have had it to downshift hard enough to squall the tires. No codes, no trans slip nothing, acceleration is smooth as butter.
Mine never did it for the longest time. Not like this only on the 2-1 downshift intermittently. Will try the speed sensor I think and see. Maybe someone out there has an answer hahahaI have replaced the transfer case speed sensor. I have also replaced the slip yoke with a nickel plated one, nothing helps. I think these built transmission are just tight enough that sometimes on a downshift it suddenly takes up any slack in the driveline causing it to jerk. The weird thing is some of them don't do it, I don't think your ever going to get a straight answer on this.
That's good to know mike, I changed the fluid very soon after it was built and then about every 30-40,000 miles after that, and I change the internal filter every single time. Spin on get's changed about every 15,000.Change the internal filter as those clutches tend to shed and restrict filter. Dex 3 is fine.