Started the C4500 this morning at about 18 degrees. Truck started normally, then after about 5 seconds, revvs to 1500 RPM and exhaust brake actuates (?) with switch in 'OFF' position.

Not liking the roaring fast idle on a cold engine, I step on the accelerator, and idle comes back down to normal. After a few seconds, it revvs back to 1500, and exhaust brake actuates...

5 minutes or so of this, and finally the truck is warm enough to where input from the footfeet keeps it at a more reasonable cold idle.

I have heard of cold high idle settings, but this seems WAY too fast for a cold engine, and wondering what the exhaust brake acutation is all about?