Grimlock was a construction by fellow Transformers, sort of like a prototype.  The first TFs made by TFs, so to speak.  Making a human would be relatively simple, given the right mechanisms, and at that level of technology we could even make a rudimentary nervous system - but making it work as efficiently as our own would be a different issue.  Stuff all the grey matter in there that you'd like, but getting it to work like a real brain would be a toughie even if we had the ability to create skeletal, circulatory, muscular, etc systems.

It's a deeper issue than that, because Megatron (re)built the Constructicons, and they don't have any mental problems, besides being bad guys.

 

If we're going to talk mythology here, then it may be a simple issue of "armor plating is too thick." Meaning there wasn't enough room for ALL of the components that make a working TF brain, so Wheeljack was forced to nip a few pieces here and there, enough to get it working, but not enough to provide normal TF intelligence. Wheeljack then improved upon his own design to enable the Dinobots even more reasoning power.

 

And I didn't mean he had an inferior voice box. I was more along the lines of comparing them to a mentally handicapped human. Assuming souls actually exist, do you think they would be the same for everybody, besides little nuances? Like every part of a machine has a different pattern to the molecules, yet they all look and feel exactly the same, this is how I imagine souls to be. So, when a human "malfunctions", it's not the soul's fault, but rather the shell the soul has been placed into, and the same theory can be applied to TFs and Sparks.

 

For instance, you get in a car accident, and you suffer brain damage. Are you any less of a person because of it? Perhaps in your daily life, but again assuming souls exist, your soul is now handicapped by your brain's inability to run efficiently. The same thing happened to Grimlock, only on a much bigger scale, considering that he didn't even have a body anymore.

 

In the case of Grimlock's New Brain, perhaps the energy fluctuations(if I'm remembering the episode correctly) enabled Grimlock to over-clock his brain, simulating normal, and even enhanced TF brain activity. How he "gave" this intelligence to his creations, however, I can't really explain, besides perhaps Grimlock transferring his acquired knowledge to whatever it was he created(I can't remember now, a gestalt, I think), the act somehow reversed the over-clocking, reverting Grimlock back to his former state, which he never really left.

So Grimlock has a speech impediment?

 

There are plenty of people who stutter but it does not make them any less intelligent. Most of the time people with a handicap are much harder and determined workers than those who are perfectly fit.

 

I think the Dinosaurs had small brains so the same went for the Dinobots made a lot of sense. If you are strong and nearly indesctructible then why do you need to be smart? I would be nice of course but not really a nessecity.

 

And why would a Transformer not be able to develop. They have plenty of human traits so I would think they could also learn new stuff and increase their intelligence.

 

I mean, in Terminator 2, the T-101 learned stuff and actually learned the value of a human life. Now if only humans could do the same.