Be sure that you have properly bled the trapped air out of the 5.7. Below is a procedure I have successfully used numerous times on my '06 5.7 Daytona Hemi:
It help to elevate the front end (I like running my 5.7 '06 Daytona up on ramp stands), check to verify that the new t-stat is installed with the jiggle vent valve up in the 12 o'clock position. Before I warm up the engine, on my '06, there is a 1/4" threaded plug on the housing that I remove and install a threaded barbed fitting to which I attach about a 6 ft. hose, and carefully route away from moving parts out the front to a clean empty bucket. I stuff a bolt into the bucket end of the hose until the engine warms and the t-stat opens, all the while keeping my burp funnel filled with coolant mix. Once warm, wearing gloves, I carefully use a pliers (hose and coolant will be HOT!) and pull the bolt to allow trapped air and coolant to drain into bucket while keeping the funnel topped off. After a few minutes of revving and looking for air bubbles in the bucket, I carefully pinch off the hose, block it with the bolt and shut off the engine. Once cooled, I remove the hose and barbed fitting, replacing it with the 1/4" threaded plug. Check your coolant level the next morning and top off as needed.
Also, Google a Lisle funnel kit at auto parts stores like O'Reilly's, etc., even on Amazon. Best filling funnel for these.
As for plugs - all 16! - keep in mind that OE plugs are copper on our older Hemis. Look for the usual - any porcelain cracks, oil residue/crud fouling the tips, excessively worn tips, and as they go past the recommended 30K mile mark change, the gaps tend to widen quite a bit, which can also cause mis-fires. Make sure they are the correct p/n as well, and when buying and installing new plugs, NEVER trust that the gaps are correct out of the box. On average, out of 16, I usually find 1 or 2 with wrong gaps that need adjusting before installing.
