Current USA 1/15hp chiller issue

[balistidae]

I am running this chiller on my jbj 28g hqi. I have the temp set at 80 and the temp differential set at 2 degrees.
When the temp starts creeping up on the scale the green (chill) light starts to blink at 82 and the chiller wont start until 83 degrees ( should start at 82). It then proceeds to chill the tank right down to 77 degrees (should only chill to 80 degrees).

I know this temp swing is terrible. Has anybody heard of this before or have any ideas? Thanks!!!!