I am wanting a set of 275's for my truck, but I want the same height as the 245s on it now. Any help on which size will work? It's a 17" rim by the way

 

Are the tires you have now 245/70's? If so then a 275/60 17 is about the closest to the stock size as you're gonna find. Its about 29.9 in. vs. a little over 30 in.

 

285/60/17's (30.46 in)are almost spot-on with the height of the stock 245/70/17's (30.50 in.) on my truck. 275/60/17's are 29.99" tall, so you would only give up half an inch in height.

From reading on tire-rack or some other such site, the minimum width for 285's is 7.5", which is the width of the standard '05 chrome steel Sierra (and I assume Silverado as well) wheels. That's probably what I'll end up getting when the stockers wear out.

EDIT: Here's a LINK

 

The 275's will just be a little wider tire!