40 % wear on 37" toyos only after 8k miles, WTF?!

[kalantar]

I installed 20 inch rims with 37x13.5 Toyo MT's. The front tires would rub a bit so they tweaked the torsion bars on the front end. They told me to come in and rotate the tires every 4k miles (which I forgot). I take it in and now the front tires have 60% tread left and the rears are decent. Clearly by tweaking the bars this effected the tread.

Has anyone else experienced this? What are the solutions?
My original Hummer tires easily lasted me 45,000 miles, at this rate the MT's wont last even 20k miles.