Lately, i have had some difficulty with my transmission in my 92 FJ80. Sometimes when i shift from park into drive, the truck will shift but will not move forward without using the accellerator. when the truck does move, there is a fairly loud clunk and a jolt. I checked the fluid level but it seemed OK. I shifted from low to high but that did not help . the certer locker is not engaged (at least the light is not on). Any ideas?