In addition to Cliff's questions:
Do you add boiled sugar water to bottling bucket and rack on top to mix well? Or do you individually prime each bottle? (you want the same amount of sugar, exactly, in each bottle)
When bottling, are you filling to the brim of each bottle, then removing the wand so that there is the same amount of headspace in each bottle? (the amount of headspace in a bottle affects level of carbonation...)
Slightly off flavor + overcarbonation screams "infection"....if you have a mild infection in some bottles, that will produce extra CO2 and cause the "gushers" you seem to be referring to...maybe you just didn't quite sanitize well enough?