I have a brand new High efficiency furnace/air conditioner. The last couple days, it has had a hard time getting down to the setting on the air. Downstairs the unit and pipes are covered in condensation. Please help.

I have a brand new High efficiency furnace/air conditioner

Call the contractor that did the install. It should be under warranty.

Your basement must have a moisture problem. Cold duct attracts water vapor in the air.

Put a dehumidfier in the basement.

Is the duct work insulated?

I hear constant drips in the sealing area where the AC flue is installed. There must be some condensation. How can this problem be solved?

Ac flue,, I`ve never seen a ac with a flue on it,, you are probably talking about the furnace,, furnace flues none that I`ve seen don`t have condensation,, but again as someone said before the installer needs to look into the problem as its his job to make things right. You don`t want to let the dripping ruin your ceiling