Q: What is making my front end vibrate?

I would first test the motor or transmission mounts. If it is not the motor mounts, the vibration might be arising as engine load and speed "interact" with the gearing at that particular speed causing a dynamic balance issue. The imbalance (vibration) could even be the result of worn out parts causing the usually undetectable residual imbalance (i.e., the amount of imbalance that is always there but is held in check by the designed rigidity of the overall assembly) in rotating parts such as axle joints, shafts, and gears to become apparent. Wireless, electronic chassis ears mounted on or near suspect assemblies can sometimes point to the general area from which the vibration could be originating. If the source of the vibration is really hard to find, there are also frequency analyzers which will decompose the noise coming off the vibration and associate that noise with the most likely or characteristic mechanical parts, giving you a needed clue. Faulty motor mounts will cause the vehicle to shake under certain operating conditions, such as the ones you are describing, so that’s why I would start the there. If you need an expert to evaluate the mounts, rule them in or out, or continue the diagnostic from there as needed, by all means contact a certified technician, such as one from YourMechanic, to get your vibration issue resolved.