A lot of times parent teams instruct minor league coaches and managers not to allow players to run wild at the AA and AAA levels.
To illustrate this here are the number of players at each level that had more than 50 SBs. The high in in parenthesis:
AAA: 0 (46)
AA: 2 (68)
A+: 5 (63)
A: 5 (87)
If you look at distributions you'd find that as you move up in class the range gets smaller and the mean gets smaller and the variance gets smaller. That chart will hold to form if you do it with 40 SB, 35 SB and so on. One explanation for this is that teams want to make sure that their prospects at higher levels are stealing correctly. That is why Felix Pie, for example, was sent to the Arizona Instructional League to work on his base stealing ability.
So, after a lengthy digression, Pie is not switiching from speed to semi-power. He is and always has been a five-tool player. The power has always been there in his ability to drive the ball into the gaps. It's only now that after adding some weight and muscle he's able to drive it over the fence.