I am looking for a more efficient way to train my abs.
Is there an exercise that works both the upper and lower abs at the same time?
Yes, the incline leg raise.
Lie on a 30 degree angle, incline board, your head at the high end.
As the feet come up, lift your upper body off the board and crunch your abs together. This works both the upper and lower very hard. Try 5 sets of 12-15 reps.
Get a contraction on each rep.