05' build ISX 15, in 06' model KW.

[Chadster]

Hey y'all,
I'm new to the forum and to Cummins, been running pre-egr Cats most of my 30 year career. I got my 06' T-600 this past Oct. I don't know what an 870, 871, etc is and don't know what my serial # is. It's not on top, side front or anywhere but I'll see if the KW parts dept can look it up. What's got me concerned is the cold start ups. Fires right up but stumbles, runs rough, in constant and shakey. It sounds like it wants to cut off but doesn't. So I give it a minute, feather the throttle lightly and finally set the cruise to 1000 rpm where it levels out a little but not completely. During this time it's putting out blue smoke but not heavy. After the temp gauge moves up to 100°F or so it gets better and once it's up to 120-140°F and ready to roll it's perfectly fine and runs like a beast and the smoke clears up. I was told that it's got a tune on it but that tells me nothing because there are so many different kinds of tunes out there that it's hard to say what this particular tune was trying to accomplish or if the tuner knew what they were doing. I also have read a lot that ISX'S like the higher rpm and do better both efficiently and powerfully at higher rpm, between 1600-1900. Which doesn't feel right to me but doesn't mean that it's not. As I've spent most of my career running CATS at around 1500rpm and getting close to and sometimes over 8 mpg running them that way. I have a 13-spd with 3.70 rears and 67mph it tachs out at a hair under 1600 rpm. So any advice or suggestions about this motor would be greatly appreciated. Stay safe out there drivers and thanks in advance for your suggestions.