I say replace your coolant temp switch? only because it is not setting high idle like you want.

honestly though, i dont think my car peaks at 1450 on cold start. i do get about 1100 high idle for a short short time, and then it drops down to about 900. I have an 09 though. How quickly do you expect the alternator the charge the battery. many alternators dont give more the 13v at idle... if you start driving sooner an not idle the car to warm up the issue would go away.

also if you replaced the belt, great, but if you didnt do the tensioner, would you expect it to tighted the alternator contact for slippage?