I am flying a PA28RT-201 and we fly it on the EGT to obtain best economy. Havent had any problems with the engine shaking itself apart and we seem to be getting consitent fuel flow figures by running it at this. Yes we do lean below 5000' as well, its not alt dependant!
I could of course go back to Piper and tell them there is something wrong with the engine as the vibration is missing
If your fuel planning is so tight that you are out of fuel before you reach your destination then suggest you are better driving or let someone who can flight/fuel plan properly do it for you!!!
Julian.