I have an 03 silverado and just recently took it into the dealer to have some warranty work done on it, after getting the truck back, had it delivered to me by a friend, now the service brake system light is on along with the abs light and the brake light. They did not touch the brakes at all, the only thing that i was told they did was adjust my speedo to accomidate for my larger wheels, which i did not request, could that be the problem?

Very well could be. Take it back and tell them to check things out.
If they messed with your speedometer or speed sensors and you did not ask them to.
Tell them to fix the problem on there dime.
Let us know how it goes.
MT