GM-GMC: p1878 & po452, driveability problems, transmission code

Question
I am asking abt the p1878 code. transmission??
and the p0452 is the evap? these cam on together..what is going on?

Answer
The two trouble codes are not likely related at all.  It would be important to know which code was current and which was history or if they were both current etc etc.  I would hazzard a guess that the evap code was likely current and the transmission code was likely a history code.  I would clear the codes, tighten your gas cap and drive it.  If the light comes back on read the code and see what you get.  I am assuming you are not experiencing any driveability problems (transmission wise) that would lead you to believe that you do actually have a problem.  If I knew what vehicle you had I may have been able to give you a little more info.  
Hope this helps a little.