I just did and engine replacement on my millenia it has a 2.5l DOHC miller in it. It ran rough for a couple hours and now it will run when it wants to basically. I've replaced the cam sensor and the crank shaft sensor. It ran for an hour, then it lost spark. The next day it ran for about 5 minutes and lost spark. Has anyone had this problem? I'm lost to what it could be

 

Sounds like a weak ignition coil. Have the spark strength checked.

 

Also check wires and dist.cap for spark leak-run in dark, open hood,and look around wires and cap.