Heater blowing Luke warm air but never gets hots?

sounds like an air pocket in the coolant system

I've had this same issue on another type of vehicle. It turned out to be the "blend door". It is mounted near the heater core up under the dash. It is controlled by a motor that adjusts its position according to the temperature setting you select. It can close off the air to / from the core or open it up partially as needed to match your temperature setting in the cab. On mine, the door was broken halfway off and we ended up with lukewarm to cool air all the time. I had to go through the glove box (cutting a hole in the back of it and replace the door arm assembly mounted on the blend-door motor shaft). That was on a Jeep. Better than pulling the whole dash out!