NV3500 issues

So I have had an issue and rebuilt my transmission about a year ago. The mechanic shop checked the fluid and told me it was full…it was not. Bound up every gear on my input shaft so I was lucky enough to have been able to find a used one nearby for sale. Put it in and now it goes fine for a few months and then starts making noises and grinding as soon as I let off of the clutch and sometimes while I’m holding the clutch really bad especially if I am coasting. Anyone have any idea what my issue might be?