Some people note a harsh bite from carbonic acidity (at least, so I've read) when the beer is freshly carbonated. It would seem that the common experience is for it to be harsher in that first week on forced CO2, and significantly better by week 2 or 3. It could be a sanitation issue... it could be that the beer is going bad from a bug, but if it were me, I would manually vent the beer a bit (maybe several times) and store it at appropriate temperatures for a while, and then try it again on a little less CO2. But it's purely guessing on my part. I would think that all of your possible problems are A). infection, B). chemical contamination, C). problems with your CO2 levels, D). dirty lines... just spitballing.
The 170 mash is history... if it was good after you carbed, then you like the product. Getting the temp too high stops some of the enzymes from doing their thing, thus limiting how much fermentable sugar you get... it should probably make the beer darker, and maybe maltier/sweeter to some extent.
Good luck! I'm sure you'll get some awesome pros here to throw in their two cents!