Our experience has been that rodent tissues process better on a 4 hour or 
so
"short run", unlike the routine overnight schedule used for human tissues. 
Over and above that, we still have to dicker with the blocks like soaking 
them in water or cutting them at room temperature. On occasions we have 
trimmed away excess paraffin from the block so it is mainly just tissue we 
are cutting. 
   Cindy, you don't mention the schedule you are using, but the tissues may 
be over processed. Good luck!

Michael Titford
Pathology Department
USAMC Mobile  AL