Go with your first Instinct. I believe ATS has done the most thorough job of engineering of all the Performance Trans Builders. I've had my ATS Stage IV in for almost 2 years and it is awesome. I would go with ATS again in a heartbeat. I don't believe you can beat Clint & family's cust. service, the ATS engineering or his dedicated employees.
I've only got about 30,000 miles on my Stage IV, and it is simply the Best Think I've ever done to the truck. You won't go wrong with their stuff.
If you want to call ATS, their number is 800-949-6002