As stated in the owner's manual it is common to have difficulty into switching back into 2wd when that occurrs you stop your vehicle and drive backwards for at least 10 feet then switch back into 2wd.Also when driving forward in 4wd high accelerate quickly and let go of the gas pedal during that sudden deceleration press on the transfer case shifter and you will see how easy it is.
Also are your front and rear tires the same size and worn the same amount? even slight differences in diameter can affect driveline binding,which is common in a part-time 4WD system like Toyota uses in the 4-Runners/pickups and Landcruisers.Are you driving on high traction surface (like pavement) when trying to shift to 2WD? If so, try to shift before you get to pavement and while driving straight forward.
Sidney
Repairs tv's,vcr's,home/car audio out of my home
E-mail:sidneybek(at)yahoo.com
Dartmouth,Nova Scotia
Canada
1985 Toyota 4-Runner,22R-E,W56,RN60LV-MSEK,rusted rear step/towing chrome bumper with 241 000 KM