1997 Jaguar Vanden Plas loss of power, stutters when accele

I found some water in my oil when i checked the dip stick! It stutters when under heavy load like going up a hill and from a start! if i shift to second or third it tends to run better! I checked the spark plugs and cleaned and re gapped them...ran much better but still not where it should be! Before i dig in and replace the head gasket is there anything else I should be looking for?