My goodman furnace has begun to roar like a large farm tractor when it starts and shuts off. It seems to be running and heating properly. Could this be too much gas pressure?

Probably not a gas issue. Might be a blower problem.

Remove your air filter and tell us if the noise goes away.

Make sure the blower cage isn't hitting the enclosure. Some Goodman units have Chinese motors with mounting brackets that I have seen broken off.