SMS Delays

We have been experiencing SMS delays for the past 2 months now. Usually starting around 10AM CST our driver's messages start getting delayed by 15 mins up to over an hour. Some messages that were sent later are received 1st creating very confusing communications.  Anyone else experiencing the same issue? Tech support hasn't been much help as they themselves haven’t figured out what is causing the delays. The majority of the delays have come from contractors who utilize T-mobile, AT&T and at least one on the Verizon network.