No, the 300 is a different model with a smaller battery pack.
It is humorous to me, to see the comments about vastly reduced range in the cold. For an 82,000 pound truck that is very aerodynamic and looks to be airtight and free of chilly drafts, the power needed to heat the cabin is likely a rounding error when compared to what it takes to propel the truck. Also, the guys at Tesla aren't much for leaving KWs just going to waste. When being discharged, the batteries will give off a bit of heat and may even need to be cooled a bit. Latest model Teslas are heated and cooled with a heat pump, which is vastly more efficient than the resistance heaters used in older cars and probably most of the electric busses. It seems likely to me, that the battery heat that would otherwise be wasted will be used to heat the cabin. Details on the truck are still kinda sketchy but I've done a bit of reading and nowhere can I find any folks involved with the semi that have pitched it as a long-haul, over the road truck. The truck was designed for the major part of the Class 8 market, which happens to be the medium range trips. I've heard rumblings about the weight of the tractor with a full battery is going to be somewhere in the 18,000 pound area.