stalling

hi all, i have a kioti mechron 2200 that is in my shop for repair. When i start the vehicle it runs perfectly in neutral, but as soon as i shift in high it grinds shift past that into low it stalls and does the same when i put it into reverse. I did some inspection and read a couple forums...

2014 Kubota, I cleaned fuel tank, changed fuel filter, changed air filter, replaced fuel pump, added new diesel fuel (just a little to test), I am baffled at why this is happening, but I am positive someone else will know. I appreciate any suggestions, thanks in advance. It does it at idle...