I have had problems with a high GC PCR. I got it working by doing the
following. Design your primers with high Tms (round about 78degrees C).
Get hold of a highly thermostable enzyme (NEB do an enzyme called Deep
Vent exo-). Set up your rxns as normal and cycle as follows 98C for 1min,
anneal 1min and do 30 cycles of this. Taq will not survive 98C but Deep
Vent will. Consequently you get high yield PCR from your GC rich
hope this helps