Our current set up is listed below:
2000/starting chips (20 @$25, 10 @ $100, 1 @ $500)
20-min. levels
15-min. levels for final table

25/50
50/100
75/150
100/200
150/300
*remove $50 chips*
200/400
300/600
500/1000 ante 100
700/1400 ante 100
1000/2000 ante 200
1200/2400 ante 300
1500/3000 ante 500

The tournament has between 25 and 30 people and we can't seem to keep to 3 hrs. The tourny ends up taking between 5.5-6 hours. Do you guys have any suggestions as to how we could alter the structure in order to keep it between 3-3.5 hours. Thanks for the help!

Make all the blind levels increase at 15min intervals will reduce by 1 hour... I think reducing everyones chip count to 1500 will still start everyone out w/ 30BBs, and should cut a significant amount of time off... Either that or take out the lowest blind level, but that'll only let everyone (with 2000 chips) start w/ 20 BB... Makes the play a little more "allin" intensive, as people will be feeling the pinch from the beginning...

I'd suggest tightening it up in the middle, as opposed to the beginning -- that way people get a chance to play a bit without worrying about busting right away, but they can't sit around once the blinds start increasing. Something like 100/200 to 200/400, 400/800, 700/1400. That gets rid of a couple levels.

Trying to keep it to 3 hours with that many people pretty much guarantees it will be an all-in fest at some point though.