Syncro worries on fresh rebuilt 833

I just rebuild my 833 for my Duster. I purchased a complet kit from Brewers including new syncros. I have had issues with the OD 833 I installed when I restored the car and just got the new 833 installed. All seemed to work fine. I could shift from 1st to 2nd with no issues and if the rpm is down below 3000 I can get up into 3rd and 4th with no issues. But if I let the car spool up in rpm and try to shift harder,I get a gear bump going into 3rd and 4th. I also have to double clutch ti get into 3rd unless I am down around 30 mph. Any Ideas? Is there any kind of break in period or maybe some sort of gear additive to help the cup work better?