LQ9 misfire.. No codes or CEL

[Chvy2NV]

What's up guys. I have a 07 NNBS with a Vortec MAX 6.0L and I seem to have a misfire at idle or reverse. Once the truck is going. It seems to be just fine. Ive had the truck 2-3 months now and Ive read endless threads and can't seem to pinpoint what could be causing this. I've had the truck plugged into a code scanner and have gotten 0 codes or CEL 's.
I called friend of mine which is a service manger at a local Chevy dealer and he says that it's completely normal. This is not what I wanted to hear... After trying to convince myself that this is "normal" for the past few weeks I took it to another friend of mine which has had his share of GM vehicles.
After sitting in the truck for 30 sec. He says to me. This **** is broken... There has to be a problem here. There's no way this drove off the lot like this. Which brings me to writing this.
What do you guys suggest I try next?