Your not actually cvomparing GameMaker6.2 to Truvision6.2, are you? I don't think GameMaker was ever intended to do 3d. I mean, it wasn't GameMaker's primary purpose. Yes, it can do 3d. And yes, if you are extreemly talented, you can actually fake some pretty decent 3d. But, that's not GameMaker's purpose.
I have GameMaker. I still use it from time to time, just to make quick games, when I'm bored. Not a bad engine. But I plan soon to pop out games in TV3D as fast as I have in GameMaker. What I'm working on right now, is tools in TV3D to help do this. The Biggest Tool I'm working on:
FigureEditor. Next project I'll be working on, I General World Editor (GWE).