2.5" spacer in a 2wd works. thats what i have in my 2004 double cab. works great. then again its just a tow vehicle. ANYTHING bigger will affect the upper balljoint in the upper control arm. if you want to go bigger might as well go with replacement coilvers from fox,king, icon, or SAW. and get the 1.0" - 1.5" uniball upper control arm so it'll fully cycle correctly without breaking the top half of the spindle. which ive see many times.