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It's all in the tuning and programming.
Most 4L60E's have an issue of not shifting from 3rd to 4th at WOT. This is one of those monsters that has been plaguing F-bod guys forever.
The solution is to first adjust shift points based on rpm. This will not fix the problem however.
Then in the tables you move to actual mph shift points. To fix the problem you have to adjust the mph shift points down until the problem goes away. The only way to do it is to find a flat open area and do WOT runs and adjust accordingly until it shifts well at WOT.
Don't know if that's what your question was leading to, but that's the solution anyway.