i hate to be the bearer of bad news........
Your overhead computer is VERY inaccurate when you start chipping these truck, it wont display anything even close to what the real distance is.....
And a tire 10% bigger than stock will probably throw it off 6-8 MPH......which is a big differenc it MPH calculations......
Sorry buddy, no way in the world your really getting 40, thats just not possible.....