2008 freightliner Columbia detriot 60 series heat up problem

I have 2008 freightliner Columbia with detriot 60 series moto with EGR and DPF delete. 2 weeks agao im having cold air in cabin cold than A/c air and i saw my temp gauge going up more than 220 and then suddenly I have hot air in cabin and temp gauge going down at normal No Power loss at all its doing same thing after 5 to 10 mints goes up and then came back normal. I CHANGED thermostats both , changed water pump ,washed radiator, change coolant temp sensor , change air compressor But i feel like I still have same problem but now when I have cold air in cabin temp goes to 180 and then after 5 or 10 mints have hot air in cabin and temp came back to 175 I didn't check with load trailer but im worried may be its still doing same temp goes up and within 10 mints its came back normal ,Please help me in this what I have to check and what I have to change one more thing I saw litlle pressure in coolant reservoir now I think its normal . No power loss, no coolant in Oil I dont know what to do Please help

 

Yes fan working good and I turn it on manually when temp is normal and while fan running temp goes up and then came back normal and its happen within 10 mints keep doing heat up and coming back normal.

 

But why its heat up and then came back normal if its head gasket it spouse to be heatup all the time when temp goes up why its came back normal and again within 10 mints up and then normal and why i have cold air in cabin. When cold air start in cabin heat going up and withn 5 to 10 mints hot air came back in cabin and temp going down if its head gasket then why temp going down? And one more thing in morning I start the truck after 30 mints i check radiator top pipe is cold and lower pipe litle hot and after driver half hour i saw both or same hot but not that much hot i can hold in hand.

 

Can you please tell me where is air controlled heater valve so I can change my self or atleast i can see it if there is any problem with it before head gasket work I want to check air controlled heater valve.