have you noticed lighter abv, sessnet?
maybe the thermometer is starting to display a higher temp than normal, resulting in a lower temp than you are used to at 300. that or obstruction of the airpath.. maybe check your screens to make sure they aren't clogged?
maybe you are using a different temp setting on your range than you had before... see, I know that with my bigger hotter torch, the display temp will continue rising to 325-330 when I stop at 300. However, with my smaller benzomatic, the temp will not make it past 320 if I stopped at 300. if you had used a hotter setting when first experimenting with the range, and the block temp was hotter than listed on the thermometer, due to the lag time it takes heat to travel from the block to the thermometer. then when you dialed down the stove/range to a temperature closer to 300, there was less lag between actual block temp and the temp displayed on the screen because it was not heating up as rapidly. so if you had been using a hotter range temp before, you could have been hitting it closer to 320, because there is a lag between heater block peak temp and thermometer peak temp. lol if I did a bad job of explaining this, somebody who is more eloquent with words should elaborate.