Its not all about keeping at 2k. There are seperate techniques for acceleration and cruising:
Your gear is to get into higher gears as soon as possible. Lift off the accelerator pedal when you reach the minimum shift speed. This way the car will shift quicker, spending less time in the fuel consuming lower gears. The minimum speeds are: 2nd at 10 km/h+, 3rd at 32 km/h+, and 4th at 52 km/h+.
Your goal is to maintain torque-converter lockup. There are 3 modes for the operation of the torque converter:
1-fully fluid, AKA slushbox mode. For the same gear and speed combination, the RPM will vary according to throttle input. All gears use this mode.
2-semi-lockup mode. The RPM will drop around 200-300 revs ( going from 1700 to 1500 for example), for the same gearing and speed combination. Its not full lock up mode, however, as you can see when you lift from the accelerator. The RPM will drop a further 200-300 revs, which shows that the TC wasn't fully locked up.
This mode is only noticeable in 3rd and 4th gear; I couldn't actively use it in 1st and 2nd. That's why it is important to get to at least 3rd ASAP.
3-full lock up - the transmission now behaves like a manual transmission. The input and output shaft are spinning at the same speed; there are no parasitic losses to the transmission. Most of the advantages of MT's are lost at this point. This mode is only available in 4th, at speeds over 70.
Even at speeds over 70, the car may sometimes go out of lock up, like when going up an incline. I counter this by building my speed up before hand, and using a light throttle pressure for the climb. Even then, it periodically goes out of lock up. I just let up on the accelerator for a second and press it back; this locks up the transmission again. In general, you don't want to be going less than 75 km/h on GT road/ m-ways. It is actually better for fuel economy to speed up a little (on automatics). Generally, 80-100 km/h is good for fuel economy.