You can get several types of auto deflators. Staun makes them. There are also a host of others. They generally cost about $50. Do a search here as this has been researched pretty thorougly. I use a $1 valve tool that lets out the air (not unscrew the valve!). I put 2 on at a time and just keep my eye on them. Never had a problem. Takes about 2 minutes a side. Saves me $.
As far as pressure, I usually stop at about 15lbs. I had a tahoe and now a pathfinder, never had an issue. I would not go much higher, and would be afraid of popping a bead lower than 15. Just my .02