How are you cleaning your filter, and how often? I know Sanyo recommends every 100hrs, to vacuum the filter, I also take compressed air and blow from the opposite side to blow the dust back out from the way it enters the filter. A lot of times a filter may look clean, but it still is dirty.

75degrees should be fine, but cooler may help if you can make the room cooler. If the projector can easily be moved, you could try taking it to a cooler room in the house and see if the fan picks up speed.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85