Bed side exhaust question

[kill_burst]

I recently installed a bedside exhaust. Everything came out looking good. I originally had the exhaust tip facing the wrong direction which caused some issues when driving about 40mphs. I’m guessing some major back pressure. I fixed the exhaust tip and the motor is much smoother now at higher speeds. However I still get some minor vibration when I reach around 55 mph and cruise for about 5 minutes. Before new exhaust it had never vibrates like this. Running a magnaflow glass pack, no cat. Any ideas what this might be? Still getting minor back pressure? Thank in advance