Does it shift into any gear OK with engine off?
And if you start truck in 1st gear, clutch pedal in, can you shift it once you are moving?
If so then clutch slave or master is the issue, not transmission.
And because the slave is the hardest to replace that is the usual problem, lol.
But check clutch reservoir to make sure it isn't dry, if it is low you may have some air in the system and have to bleed it.
Air compresses more than hydraulic fluid so if there is air in the system the clutch disc can not be fully disengaged with pedal to the floor, so input shaft never stops spinning and transmission can not be pushed into gear while stopped.
Once you are moving the output shaft(driveline) is moving as well so trans can often be shifted, although it would feel harder to shift
Last edited by RonD; 11-28-2014 at 11:08 AM.