Hi,
I would read the Hatching 101 in the Learning Center first.
When using a thermal (still) air incubator I always move the eggs all over the bator so every egg has an equal opportunity to different temps within the incubator. Many times per day, in fact.
Lower temps, depending on what they are, can lead to developmental anomalies, late hatching, etc. As you already know.
Higher temps can, and per my experience will, lead to early hatches and sometimes the chicks can grow so fast and large that they may have problems getting into proper position for hatching. So you would want to keep an eye out for 'malpositioned' pips too.
Are all your eggs from the same breed of chicken? How long were they waiting before you set them? (Collected at the same time, or over a period of time)
How did you store the eggs while waiting to set?
How are you turning your eggs?
Are you rotating them around in the styrobator?
You want to make sure you don't have early, middle stage or late stage 'quitters' as well.
Will look forward to other's input and wish you the best for a healthy, happy hatching.