Overhearing issues

So its been a long time back and forth trying to fix my overheating issues with the jimny (M13A non vvt) 2002 manual. Had a lot of problems and mechanic fixed 2 freeze plugs that was leaking on the right side of the engine block and the coolant loss stoped. I also changed the radiator cap but the overheat was staying . So i thought that the problem was the stress of the engine cause i had steelies 8" and At tyres 215/75/15 . Finally changed them and got back to oem aloys 5.5j and the car is running smoother. Then i checked the viscous fan and was working properly . Lastly i start a whole coolant flush to use better coolant and clean the system cause the heat core didnt have much heat . The flush helped a lot and it took me 6x4liters of distilled water to clean fully the old coolant and the trash that was in the system. Now the car is a lot better. In the city the car is not overheating the temp gauge is in the middle all good . Yesterday when i started to go to the village the car on the hill started increasing temp . On 4gear the temp was going up but in 3rd gear the temp was going down . I was also checking the temp with an ecu reader. When the car was in 104 celcious the temp gauge was in the middle  but when the max temp got 105 degrees the temp gauge was going above middle . Anyway on 3gear it dropped to 98 degrees. 
I also live in cyprus were is pretty hot 37-40 degrees iin august. So my last thoughts are to change the termostat( i dont think is the problem cause it only overheats on hills and and on 3rd year the temp drops ) . Also i don't think is a head gasket cause no oil mix with coolant also no coolant loss and no fumes from exhaust all work fine . 
Is there a possibility of a bad temp sensor ? ( should the gauge get  a lot above middle if temp was 105 degrees?) 
and lastly are there any other plugs on the left side of the engine block to change for possible minor coolant losses ?
What should my next step be ?

(Sorry for the long paragraph is just the frustration coming out)
 

My first question, and yes, I did read your post, is what makes you think it is overheating?

It's no longer loosing coolant, in the city it is not overheating, 104~105*c is not an overheat condition.

What is the symptom that makes you say it's overheating.

Hey fordem
That is what i have trouble understanding
Cause the ecu reader that i connect to my phone on hills and 4 gear showed a max temp of 105 degrees but on the car dash the temp gauge got well above middle . I all my other car the temp gauge is staying on the middle but on jimny until 104 degrees (that the ecu reads on my phone ) the sign on the dash is in the middle but when it hit 105 it get above the sign in the middle

The dash gauge is not a precision instrument - have you ever noticed it has no numbers?

Get an IR temperature gun and measure the actual temperature on the radiator top hose.

Has the temperature gauge ever actually been in the red section or does it just climb up a bit and drop back? The thing is the m series is usually very stable in real terms with its heat management right up until it's not. Once it's been into the red then it will 9 times out of 10 need a head gasket. You will be told that it's fine and to change the thermostat and the heater core and the coolant and the radiator cap and the radiator and everything else but it will only delay the inevitable. I nursed my last jimny for 3 years changing the above one by one but eventually I had to get it done. The actual defect was apparently very minor compared to most the machine shop usually saw but it was enough to be putting combustion gasses into the water jacket.

Hello Conev,

Your Jimny isn't overheating. 105degC on going uphill on a Mediterranean summer day is not a problem.

The main reason it gets cooler when you downshift is that the water pump is turning faster.

You should be downshifting when you go up hills as a rule, for lots of reasons. The peak of the power curve is around 4000rpm, so that is where the engine wants to be when you are making it work hard. Don't be afraid to rev your Jimny's engine.