Its too lean. If it takes off well and then just dies, its lean, you need to fatten the needle up, especially in 35 degree weather which is VERY dense air not helping the problem. Richen the high speed, dont even worry about the low speed or the pinch test, once you get it so it will not die when it starts going fast, then bring it in and do the pinch test and get it so it cuts off in about 2 seconds.

remember to turn the needle in 1/8th degree increments or LESS. A little turn goes along way with a vertex small block.
Im on my fourth Redcat with the Vertex mill and everyone of them acted that way.