Did you get the battery with the used truck? If so, I'd say it's the battery. When Lipos get old, they will behave like they are not charged, or partially charged. It'll run a few minutes maybe, then it acts like the LVC is cutting in, then a half lap later, full power again, and a lap later the power drops again. This is the sign that the lipo battery is at the end of it's life and needs to be replaced. I am told that placing the pack in a coffee can of salt water for a few days will neutralize the chemistry and make it safe for disposal.