75 degrees ambient is plenty warm for carbonation. I wouldn't skip secondary if you feel the beer needs it. You can always just add a light sprinkling of Lager yeast to the carboy the day before you bottle to make sure you have enough yeast to support carbonation, but that is usually only necessary when you lager or secondary for longer than what you have been doing.
One other thing that comes to mind is if you have a highly flocculating yeast there might not be enough in suspension to do the job properly, in that case you might want to rouse it a bit by giving it a quick stir about 20 - 30 minutes before bottling. (Any residual sediment will floc in the bottle...trust me ).
That all being said, I have had stuff take ages to carbonate. The two key factors in getting a quick full carbonation are yeast health and temperature.