burpa

I just had major breakdown after going to Carslile last week My C5 clutch stayed on the floor found the slave cyl leaking had dealer replace it along with the clutch plate and throw out bearing . Got the car this afternoon now it shifts good except 5th and 6th gear which grinds, took it back where they will try to fix tomorrow however they told me it probably was a bleeding issue , which makes no sense to me since it works fine in all gears except 5th and 6th
anyone ever run into this after clutch replacement and what was the fix .
Any help as I need to deal with tomorrow
Thanks
Dave