certain GM vehicles had the option of "2nd gear start" for many years... both FWD(4T60E) and RWD(4L60E). they automatically kicked out of it if you went past a rather large amount of throttle, but otherwise, they just make the torque converter run closer to it's stall point for a longer period of time.
depending on how the shift pattern is setup, you could see a noticable change in fuel economy, though not necessarily in the direction you want.
my 1-2 shift happens at 9MPH with minimal throttle... i can almost idle it up to that point and have it shift into 2nd. fuel used to do so is pretty much the idle fuel consumption rate. i've also played around with 2nd gear start to a degree and it takes a considerable amount of throttle to get the car up to the same speed, with the torque converter pretty much running against it's stall rating of 2100RPM. considering how much further the throttle is opened along with the significantly higher engine speed, fuel usage during this is considerably heavier to achieve the same speed.
it is great for low-traction situations though... very hard to spin the tires when the total torque multiplication is ~5.2 compared to ~9.7.