Hi Phoneman,
The slowdown is caused by deprioritization. Since cell towers have limited bandwidth, your speeds will be slowed to preserve bandwidth for customers with higher priority (Verizon Postpaid/Prepaid). This will occur regardless of signal strength.
Multiple factors can cause slowdowns to happen. If more people are in your area now than there were previously, slowdowns can happen. This is common in southern states as snowbirds move in for the winter. The increase in travel over the next few months (especially if you are near a major highway), can also impact your speeds. There isn't really anything that you, as the customer, can do to improve speeds.
