Duramax starts funny
 

Hi guys, woke up this morning and went out, turned the key, the glow plug light came on and went out normally...I turned the key and it started with an extremely high idle, it went back down, but was still very high....after about 30 seconds it dropped back down to it's normal idle...it now does it every time I start her up...what is it and what do I do? :nope:

Thanks guys!