What are the specific codes?? There are codes that are being set by both of these lights, as both are a computer system. If your mechanic has not told you the specific codes FIND another shop ASAP.
here are some shops:
The problem you describe suggests the transmission is not working properly. The overdrive may not be applying, the torque converter may not be locking up or the transmission may be slipping internally. You need to have it checked out by someone who know what they are doing. Use repair-pal to find another shop.