2007 Ford F-150 4 wheel drive only engages when stopped

Hello
I have a 2007 F150 FX4 and the truck will no longer shift into 4H while on the fly. However, when I come to a stop, the 4H engages without any issue. When rolling, the 4x4 light will come on and you can hear a slight humming noise, but it will not engage. When I first noticed this, I had recently put a small front end raise on the coil towers and anticipate this caused the issue. I could just pull these back off, but the rear end has an added leaf spring and the truck stance would look odd. Im hoping you can help me identify if there is an easy fix or way to troubleshoot the issue. Thanks.