First of all, no beer should ever be fermented at an ambient of 76 - hopefully that was a typo. Oddly enough, contrary to your post, fermentation temps have one of the biggest impacts on head retention. If you are fermenting much warmer than 68-70 degrees for most ale (fermentation temps, not ambient) then you head retention will be terrible - and so will the head aches that come with beers fermented that warm. Warm fermentation causes fusel oils which not only kill beer head but kill your head too.
If you fermented at an ambient of 76 - your fermentation temps were through the roof!!
The strange thing is that you say your head retention was great on that beer, and non existent - which is a little confusing. However, the other component of good head retention is how much yeast you pitch and, or how healthy your fermentation is. You must pitch enough yeast, that means making a starter or pitching slurry with liquid yeast.
Regardless, reading your post t appears you have sloppy fermentation practices. You need to get a handle on that. Fermentation makes the beer - and pitching temps (never pitch over 70, preferably much cooler), fermentation temps (never ferment much warmer than 68-70 - which means your ambient must be in the low to mid 60s) and always be sure to pitch enough yeast. You get those areas ironed out and you will see all kinds of improvements in your beer.
As far as the length of the boil, (if I recall correctly) a longer boil can break down the proteins that form head retention so I would say that is not an issue either.