Typically when you have acceleration problem as you are describing it can range from fuel, ignition or transmission problems. (yourmechanic.com)
The same team that got Toyota to agree to a $ 1.2 billion penalty for hiding unintended acceleration problems from NHTSA is working on the GM case. (canadianbusiness.com)
If the fuel system is clogged with excessive debris or carbon deposits, it will create acceleration problems, as will an engine misfire. (yourmechanic.com)