failed emmissions codes on 1998 GMC Yukon

Does anyone out there know what these codes mean? The emmissions place did not know?? P0155 and P0300? Trying to get an idea b4 I go to mechanic so they tell me the truth! Thanks!

1 answer
Here is some info abou both codes:
http://repairpal.com/OBD-Code-P0135-and-P0155
http://repairpal.com/OBD-Code-P0300