#1
i got some ernie ball power slinkys and i put them on my guitar,tuned them all up and the G string sounds out of tune when played in a power chord that has the D string in but sounds fine when playing the D chord(high E,B) the strings are this gauge>11-14-18p-28-38-48 can play the G string in a power chord if i tune it down a tad tho
#3
Your intonation's probably just off. Also, if the strings are heavier than what you used before, check the neck bow before adjusting the intonation.