Ok so story of my life need to get this straightened out lol. Lets review what has been done. 3 temp sensors now on a brand new OEM temp sensor. Tried 2 thermostats. Tried 2 rad caps. Tried a new rad. Recently swapped the turbo, replaced rear cam support seals the 2 red and 1 black seal. Tried a wrx coolant tank. What else is left?! Yes let me guess headgasket.

 

So today after driving for a while opened the door and noticed the fans were off. Popped the hood fans came on for a good 15 seconds awesome! What I noticed was the upper rad hose didn't feel pressurized well nearly as pressurized as it usually is! What does this tell me? Also the overflow was at a higher level then normal. What is the damn issue!!

what car and miles?

soft upper hose sounds like air is in the system, maybe there's a bubble that needs to be bled out. might be a head gasket like you mentioned, you can have a test done to check for exhaust gases in the coolant to rule this out.