Are you weighing him full or empty? If you are weighing him empty and at the same time of day, each time you weigh him, he should be around 950-960, he gained a little over 3 pounds a day for the past 5 days. If he is empty now and you weigh him in full, he should tip the scales at 990-1000, if he continuous to gain 3 pounds a day.
We always try and weigh empty, we weighed prior to the evening feeding and they had been tied in the barn all day. This lets you know where you are at and gives you some idea where you need to go, plus their ADG is much easier to determine if you are consistant on the time you weigh.