Could be the CPS sensor, they tend to cause warm startup issues when they are failing, but I am not sure that would explain the inability to rev past 4k when warm. Hopefully someone will more knowledge can chime in.
Not sure if you know, but you mentioned revving the engine after a cold start. It's better for the engine to not rev past 4k RPM until the engine has fully warmed up to the 180° coolant tick.
