Found a good deal on some Goodyear Wrangler Fortitude HT tires. They are 255's not 245's which were stock size on my Envoy. So they are 10mm wider and 6.5 mm taller. It's not very much but will it throw off my TCM or ECM enough to be a problem?
If you're replacing all 4 then no... just your speedo will be off by a small amount - about a mph at 65.
HOWEVER, the overall height of the tire will make it a little close for the upper ball joint. I think the max height is 30.5" and 255/65/17 puts you at 30.1"