Ram tranny problems

What actually controls first gear that different from the rest? I've always seen cars losing multiple gears and not just one. I'm trying to understand how it works instead of just slapping stuff into it. Anyone can throw plates and a converter in. Could the regulator/govener sensor be bad? Could it be because the abs and the computer not realizing the truck is moving until 20mph causing it not to grab first? Sometimes it the simple stuff that's gets you.