I've had a little experiance with GC rich templates, I suggest tyrying
some of the following.
1. 5%-10% DMSO in your reactions.
2. 7-deaza dGTP at 25%, 50% and 90% to normal dGTP
3. Initial denaturation for 5 min at 96 deg, and cycle at 96 deg.
4. Try pfu polymerase, it allows you to cycle at higher temps which is
important to denature GC rich templates.
good luck