damn, wish I knew more about motors. contact your builder ASAP. I know people who say 500 miles for break in and some say 15 miles basically beating the car. some even say once the oil goes through the motor it is broken in. not that I agree with all of that, but 1300 miles I would say should be more than enough. contact the builder and find out what he says.
I would do a leak down and a compressione check you prob have a bad cylinder. My hellion car only made 700 on21lbs with 7 cylinders. I had 40lb compression in num. 4 and 80 % leakdown.