Is it possible for an airliner to cruise at engine full thrust?
Full take-off thrust time is limited by the engine producer: bad things like overheating and meltdowns may happen. If you mean set the thrust to maximum allowable cruise setting: nothing much would happen other than consuming a lot more fuel than when using optimum cruise setting: fly fast enough, and the drag rises a lot without icrease in lift, due to compressibility effect. So the aircraft does not need to fly higher when going faster, it only burns more fuel.