Clif, PMD is Precision Model Distributors. Or
www.gardentrucking.com.
As for the transmissions, planetary transmissions are perfect for the trucks. You really can't beat their small compact design. I'm going to run one in my own truck as well. The one I went with is a slightly larger design, for robotic use, but not much larger. Yes, you give up shifting gears, but you know what? I had a three speed truck and I never really took it out of 2nd gear anyway. I won't miss the shifting that much at all. Sometimes simpler is better too. The transmissions with multiple gears tend to have a lot of slack in them, or backlash. The dogs that slide into the gears need to have slots so they can slip in easier, but that's where all the slack comes from. A planetary will be nice and tight, without any noticable backlash. You notice the backlash most on a 3 speed, when you go forward to reverse, or when the truck rolls to a stop. Also when going down a hill. You stop, but the model rolls a little bit further then you expected. So nothing wrong with a single speed at all, in my book.
The only thing is, depending on what motor you run, and what voltage you run it at, 16:1 might not be enough of a reduction for you. What voltage and motor do you have in mind?