I am assembling a t56 after rebuilding and replacing bearings and I am at the point to start shimming and I'm getting a little confused with numbers and decimals and zeros all over the place!

I have the t-56 manual PDF and it says:
Mainshaft: .000-.002 end play
Countershaft: .000-.002 preload

Then I search around on LS1tech and I find plenty of conflicting suggestions to this.
Some common results I have found are:
0.002-0.004 preload on countershaft
0.000-0.002 preload on mainshaft
0.000-0.001 end-play on extension shaft

What is the rational behind the tighter tolerance and additional preload? Does the break in process and relaxing of tolerances really exceed the tremec suggested preload?

Should I go the preload all around path?