I posted this in another thread
The Chrysler/Ram 5.7 is just known to have cold start "complaints". I say complaints instead of issues as it just seems to be an annoyance instead of an actual problem.
A few things to try (I eliminated it on my 5.7 Challenger)
Check the torque on your intake manifold. 100% of the cases I have seen reported show that they are loose from the factory, or they just back out over time/heat cycles. For me this also improved throttle response.
Run a good fuel cleaner. Techron concentrate is a favorite but my choice is Redline SI1 as it has more PEA in it (the main ingredient) than the Techron plus a supposed UCL.
If still on factory installed plugs, change them. This may seem a little drastic but if your really want to fix the issue then its worth it. Every instance I have seen of someone reporting the gaps on the factory installed plugs show that they are very inconsistent. I pulled mine at 20k and some were very under gapped while others were very over gapped. I gapped the new plugs myself and installed, it helped with the cold start as well as reduced my knock retard.
My car had less than 20k miles when I started getting cold start and idle issues. The combination of the above completely eliminated the issues.