Varying Carb Levels in Bottled Beer

I've bottled for the 3rd time, and after 2 weeks of waiting I'm noticing that most of the bottles are just fine, but every once in a while a bottle will be undercarbed or overcarbed. The under and overcarbed beers are drinkable, there is no acid aftertaste (like when you overcarb a keg), but the foam will come out of the top of the beer and I have to pour it in a glass.

I stirred in the 2/3rds cup of corn sugar and stirred it for 1 minute in the 5 gallon bucket.

My question is: Is it the bottom of the bucket that has more of the corn sugar and that makes the overcarbed bottles? Maybe the top of the bucket has the undercarbed bottles?

I'd like to have consistency in carbonation in the bottles.

Most likely not diluting the priming sugar evenly. I would also recommend weighing your priming sugar instead of measuring with cups. It is very easy to pack a cup of sugar more than the next one or not as much as the last. It leaves a margin or inconsistency. Once I started weighing my sugars my batches were more consistently carbed. I usually dissolve the sugar in a bit if boiling water then toss it in the bottling bucket. Then rack the beer on too of it so it mixes throughout the batch.

I did dilute in a saucepan. Your racking back idea I think will fix the problem. Get it stirred up completely.

Thanks.

Also, thinking back, I did add extra corn sugar into the bucket. I was brewing a Belgian Wheat Wit Beer and thought it needed above a 2 vol/vol carb level. I should have just stuck with the corn sugar amount that they provided in the clone kit, or I need to buy a food scale so I can weigh it out myself.

NOOB = me.