Originally Posted by shielded117

We also have the issue of the cockpits of each zord being different as well.

The best explanation (in show, of course) is that sometime between the events of T:aPRM and Shift into Turbo is that the zords were upgraded. When originally created in the movie, they were fresh off the Zord Foundry floor and could have had a few bugs. So when they make it back to the Power Chamber, they 'completed' the zords and further developed the Turbo arsenal. The seats for the zords are now the Turbo Karts, for example. Thus we also have an explanation to Kat's line about the megazord sequence being more difficult.