Repeatedly changing UIImageView image freezes - ios

Question

I create six (6) UIImageView's and add them to the view. I then create a timer running at 0.01 second intervals and incrementing the number by a set amount. Every so often the numbers just stop changing. Below is a sample of the code I'm running to better show what I'm doing.
NSTimer *newTimer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:#selector(numberTimerFired:) userInfo:nil repeats:YES]];
[newTimer fire];
// Assume that I've created six (6) UIImageView's and stored them in an array called digitImageViewArray (the right most UIImageView would be index 5)
- (void)numberTimerFired:(NSTimer *)newTimer
{
// self.currentNumber is the NSInteger property that is incremented each repetition
int tempScore = self.currentNumber;
int currentDigit = 5;
do {
int digit = tempScore % 10;
tempScore /= 10;
[[self.digitImageViewArray objectAtIndex:currentDigit] setImage:[self.numberImageArray objectAtIndex:digit]];
currentDigit--;
} while (tempScore !=0);
self.currentNumber += 133; // 133 can be any number to increment by
}
I have other conditions setup to stop the timer when the number reaches the final number. As I said, as this number goes up, whether the final number is 999,999 or 50,000 it just freezes intermittently as it rises. Any help would be greatly appreciated!
I also checked the Profile and watch CPU / memory usage. It's not even breaking 35% CPU and the memory usage is very insignificant. I've tried several fixes, such as adjusting the time interval the NSTimer runs at. However, if I leave the screen after it runs and come back… it runs smoothly with no glitching.