bad slave or master cylinder
Your clutch needs adjusted or replaced.
If it will go into gear when the engine is off but not when the engine is running, the clutch is not disengaging. It could be the clutch, possibly warped or put in wrong, or it could be the hydraulic clutch mechanism.
Vacuum lines, clutch switches, ...
Could be a broken clutch fork, linkage, or cable depending on the setup.
If it does this in all gears, I bet your clutch is shot. Other things that could cause problems are the Clutch master cylinder or clutch slave cylinder.
Could be a blown fuse, low of refrigerant, defective A/C clutch, broken or slipping A/C belt, or as simple as the wires to the A/C clutch disconnected.
A warped or otherwise damaged clutch disk or a faulty clutch master or slave cylinder could be preventing the clutch from completely disengaging when you depress the clutch pedal.
There could be a number of reasons why your truck will not shift properly. There could be something wrong with your clutch or transmission.
im thinking you need a new clutch.
it might be the slave cylinder
If you have bleed the system and If it will not go into gear with the engine running, the clutch pressure plate may have failed.
I could be wrong here but are you "kangeroo jumping" as in failing to use the clutch properly when changing gears thus the car lurches, this could be a result of a worn out clutch OR gearbox.