Question
We have two very tall sweetgums that were on our property before we built our
house.  Since the completion of the house for the past two years the very tops
of the trees are getting less leaves.  Are the trees doomed or are they just
stressed,and have the potential to recover?

Answer
Hi there. Sound like you have construction disease. Any time a house is built near trees the root system is driven over by equipment(which compacts the soil,basically suffocating the trees),the soil grade is changed and if trees have been removed remaining trees can be subject to sun scald.The only thing to do is wait. If they live for the 3-5 years than you can take remedial actions.
If the trees are not near the construction zone than one possibility is Xyella fastidiosa.(you can google this). Hope this helps,Bill