Completed furnace, maintenance and inspection. I cleaned flame sensor and wipe down furnace. I checked components and amp draws. I tested air pressure and temp splits. Furnace was overheating within about five minutes when I arrived. Upstairs vents were closed and so we opened those back up. I checked blower speeds and gas pressure. Furnace is now running with a 45° temp split instead of 65° temp split. Furnace ran for over 25 minutes before I left.