So i have a 95 honda civic coupe, b18 ls built turbo engine, with an ls trans. Trans has mfactory diff, fd, countershaft. Car was running and driving great, had third gear grind when i bought it and drove perfect in all other gears. I go home to pull the trans repair the 3rd gear grind. I installed new mainshaft 3rd gear, 3-4 hub and slider, and 3&4 synchros and synchro springs. I am 100 percent certain the trains is assembled correctly and all clearances are on the money. Tried 3 different clutches and have had 3 different specialists say everything is perfect. So now i want to make this post for help.
i will give a perfect explanation of issue
crank car, push in clutch sitting still and every gear changes perfectly and smooth i can release clutch and pull off smoothly. When i got to shift while moving i get notchy feeling and grinds into and out of any gear. The issue only occurs when wheels are moving.
next explanation.
i can out the car in gear with clutch in and car bot running, it makes the car very hard to push and while being pushed i can pull into neutral with clutch still pressed down and it gets easier to push then i can push shifter into gear itll clunk into gear and be hard to push again.
with that being said. IT IS NOT THE CLUTCH because i can crank the car and go into any gear with clutch in smooth as butter zero rpm fluctuations and zero movement.

seems as iff my issue with gear changes are apparent only when the diff is being spun by axles and The shafts inside transmission are spinning.

similar to a clutch issue but on the other end where a clutch issue would allow main shaft to spinnwith engine. This is occuring when diff is spinning the internals of transmission.

please help thank you for any help!