Slow wifi speeds on new Quantum Router.

Slow wifi speeds on new Quantum Router. Just got and installed the new Quantum Router. I have the 75/75 plan. Using wireless with me standing in front of the new router, the most I get is 48 megs down. I also have a Trendnet access point(3 years old) and I get up to 69 megs down standing infront of the Trendnet WAP. Wired connection gets me up to 89 megs down. What could be causing the new Quantum Router to be giving me such slower speeds? BTW, the Quantum router has 2 signals(2.4 gigahertz and 5 gigahertz). The only device at my house that sees the 5 gigahertz signal is my HTC One M8 smartphone. I get a full 83 megs down with that signal. The 2.4 gig signal only gets me 48 megs down. Is there a way for my other devices to see the 5 gigahertz signal? Is there a way to “speedup” the 2.4 gigahertz signal on the new Quantum Router to get something approaching the 75/75 I am paying for. If my 3 year old Trendnet access point can get my close to advertised speed of 75/75, why can’t the new Quantum Router do it as well? Thanks in advance. Navyson