The green zone is the efficient zone.
Drive in whatever gear you feel like. I personally drive in the highest gear possible, without bogging the engine down too far (2000rpm range usually). Gives the best fuel economy. Reving to 3500 or whatever is fine.
Keep in mind there is no exact science.
My 5.2L Build thread
-1989 Jeep Wrangler 2.5L, soon to be 5.2L
-1996 Jeep Grand Cherokar 5.2L, donor and rainy day driver
-2004 Kawasaki KLR650 sunny day driver
"A well regulated Militia, being necessary to the security of a free State, the RIGHT
of the people to keep and bear Arms, SHALL NOT BE INFRINGED