FG Effects of High Fermentation Temps?

[BPal75]

So I just kegged my American Wheat beer this morning. I used the Wyeast 1010 American Wheat yeast strain which I understand from Wyeast should ferment between 58-74F. Well I had some temp control issues on this batch and I accidentally let this one get too high. It fermented around 77-78F. To try to compensate for the high temps I left this one in primary longer (4 weeks) and when I tasted today it wasn't too bad, pretty fruity, but no hot alcohols which was good. However, it tasted fuller-bodied then I'd planned. My recipe on beersmith predicted FG of 1.012 but I finished at 1.018.

I think part of this could be because I did also miss my mash temps a bit on the high side (was shooting for 152 but hit 155). But I've shoot a little high on mash temps before and never had my FG off by this much, usually I can get it to within .002 of my expected FG. So my question is what else could have caused my FG to finish so high? The only other thought I had was whether the high fermentation temps caused issues? Could it have effected the yeast during the growth stage so that it was effectively underpitched (i.e. I had inadequate yeast growth)? I made a 1L starter which yeastcalc told me should be sufficient for my 1.050 OG, but that presumably assumes proper fermentation conditions.

Any thoughts would be appreciated.