Going to a five gallon boil has lots of differences. First, not sure your stove top can keep a roiling boil going, takes a LOT of energy, most people go with propane at that point. Your also going to obviously have a lot more water to cool and an immersion wort chiller is the absolute minimum. A lot of folks use a different type of chiller. The quicker you chill it, the better. Remember that with partial boils you can also get the temperature down pretty quick by adding your make water chilled. In full boils, you are totally dependent upon chillers to get the wort to pitching temps. Caramelization gets mentioned a lot here, but if you get the water to right at boiling temps, take it off the flame, then add your d and l me's, stir while pouring or dumping, you shouldn't even have to be concerned with that. If you were to just dump it all in at once, don't stir, keep the heat cranked up, then yes, your going to have those problems.