You should probably check the mechanical fan and make sure it's hard to turn when it's hot. It's supposed to stiffen up and push more air through the radiator when hot.
Cheap fix: Remove the fan and smash the front of the thermostatic housing with a hammer - not the center where the bi-metal coil is, but all around the center, dimple it in real good - makes it so it can't spin on the shaft and always pushes max amount of air. :thumbup:
If you want a good replacement t-static housing/fan....... I know a guy that keeps a few good used ones around....... :shhh: