clutch

It actually may be a faulty or worn out clutch. But, it may be the transmission also. Both will have to be removed to check and/or make necessary repairs.

I was having the same problem out of my 4WD T100. I found out from Toyota that the clutch pedal bracket has a defect that causes shifting and other related problems with the clutch system, transmission, and driveability. Toyota carries that replacement part and told me that they've had to replace them on countless T100s. If you need anything else you can reach me on this site