We are currently in Queen Creek north of you and we also notice times that the internet is much slower. We assume tower congestion as the times correlate with morning commutes, after work commutes, dinner hour until 8pm. Holiday weekends aren't good most times of the day. All the snowbirds are arriving to these areas and we all add extra congestion to the towers.
Number of bars is not equal to quality of internet. Bars only tell you how strong your connection signal is, not how fast the internet is. Completely different color of horses! You can have 5 bars and slow internet as we did at the recent Balloon Fest in Albuquerque. Great 5 bar signal but too many users!