Put it in neural, start it, left foot on brake.
What if you hold the RPM to around 1200-1500 and then slam it in gear, does it still dies?
Trying to see if the engine is just under powered or Trans is lock up as Master Tech mentioned.
Be careful with what steak said. The van could lunge forward when you put it in gear with the engine rev'ed if the torque converter is locked.
If the van is facing a wall and if nothing is behind, I would put it in reverse. But also another caution, if you do put it in reverse, know that if it lunges backward it could cause you to increase the throttle without meaning to.