Posted: Aug 06 2011 at 4:18pm | IP Logged

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Welcome to the group!

The things that make a truck better off road make it worse on road. The trucks brakes were not designed to handle the rotating mass of the oversized and heavier wheels and tires. The steering linkage is not strong enough to hold up to the added wheel weight so drive it gently or up grade it. The trucks center of gravity is now higher and chances of rolling are increased.  

All highway vehicles are suppose to pull lightly to the right. This is so if the driver goes to sleep the vehicle will drift off the road to the right. A front end alignment and resurfacing the brake discs with new pads might fix some of the problems.

Good luck.. Don S..

Posted: Aug 08 2011 at 7:27pm | IP Logged

I believe your MPG is less due to the fact that the speedometer is now reading incorrectly. Bigger tires turn slower. Check out this calculator which shows the speedo changes when changing tire sizes:

http://www.miata.net/garage/tirecalc.html

(I could not get hyper link to work)

http://www.discounttire.com/dtcs/infoTireMath.dos

Try this one. I've used it often...

Also much added wind drag from large wide tires! lakota