Big time rumble and shaking when going 45 to 55 mph, then check engine light flicker on 2001 Ford F-350 Super Duty

When I am going 45 to 55 a rumble can be heard in front of truck and will end when tranny shifts. Truck will shake for a short distance. Also the check engine light will flicker on then go out

Asked by for the 2001 Ford F-350 Super Duty
NEED to get that code for the Check Engine Light ASAP! Then you will have something tangible to trace and repair.