There are 4 different temperature thermostats available: 71*, 82*, 87* and 89*
Unless you screwed something up somehow you probably just installed a thermostat that opens up later than the one you took out. For example, you had an 82* and installed a 89*.
I live in very warm weather area and drive my cars very hard, so I run 71's in my turbo cars. I'd suggest an 82 for average climate or 87 for cold climate. If it takes too long to warm up with any of those, bump them up to the next step.
If it's heating up on the highway while in open air, the radiator is most likely plugged with bugs and debris. This would fall under the category of "air flow" that Jimmy mentioned.
Pull the radiator out, it's super easy to do. You can use a regular garden hose to wash all of the bugs and debris out of it. Just spray water through the fins and you should be able to get it clean enough to work properly this way. Spray from the back side to the front side at first until you get most of it clean. Once it's mostly clean you can spray from both sides. You are just trying to push the debris back out of the fins instead of forcing it all the way through.
Regarding the "turbo control valve", if you aren't keeping it stock (guessing not by the blue silicone hose
), just remove it and re-adjust your wastegate to the desired boost level. Install an aftermarket boost controller if you are trying to run anything more than a couple psi above stock. If you are going to raise the boost level, I'd suggest a good cbv also to help maintain turbo life.