better meliage on 97 tacoma 2.4l

i have a 1997 tacoma 2.4l automatic and would like to get rid of the cat converter for better gas meliage i have done this on a 95 corolla with great resultes hopeing to do the same with my truck, iam really suprised that it only gets about 22-22.5 mpg on the hwy i get about 21 in town after i put in irdum plugs good wires and syn. oil also would a aftermarket coold air system help?i have 80,000 on it now and it does have new 02s on it can you get rid of the back o2 and drop the cat or not? also the back o2 isnt a screw in type it held in by 2 screws to the pipe in 1997 thanks. trying to get better meliage.