Try checking the intake manifold or carby for a vacuum leak.
The vehicle would stall when put in gear would be the fuel pump. The fuel pump is very weak which would explain why in neutral the vehicle starts if it gear it would have to have more gas.
Ignition module is bad I had a similar problem on a Pontiac grand am- it was the torque inverter. It would idle fine, run in nuetral, but as soon as it was put into gear it stalled with a thump.
what causes a boat motor 40 hp to stall when it is put in gear
Is your clutch bad or wearing out ?
if it's an automatic trans, the torque converter could be faulty.
sounds like t.c.c solenoid.[torque converter clutch solenoid]
it sounds like ur clutch went out in it.
It could be that the torque convertor is locked and not slipping which it should do as the normal operation
your torque converter has locked up.... it's like having a manual transmission with no clutch.
The kick-stand switch or clutch lever switch have failed.
This is usually caused by a faulty seat safety switch.
torque converter or solenoid problem most likely if it runs out of gear ok.