I need a little 2015 performance advice

I went from the stock 265 65 17s, to Cooper AT3s 275 70 17 on stock sport wheels, I was getting 17 flat after the tires and high 19s just before after changing plugs and fluids, but my rear leafs were sagging with any weight in the back so part of the mpg gain I think was getting it slightly nose down.... I did all 3 mods at the same time before a trip up north, cat back, spacer and lift and on my first trip I average 18.6 over a 1000 miles... I used the xtp spacer, helps the low end torque a lot, before the spacer it was hard to spin the 32s off road, with the spacer I can spin the tires easy... I used a magnaflow 18 X 6 round muffler and had the muffler shop bend me a 2 1/2" cat back with full tail pipe... I put on the cat back first and helped the top end over 3000 but hurt low end... It was out flowing the engine... That's what made me put the intake spacer on, I didn't want to loose the top end but I need to fix the low end and the spacer combined with the cat back works great... I think I just sort of lucked into it.... I was still debating going to a 2 1/4 cat back for more low end but added the maf cal from urd and the extra fuel makes it run great... With my latest maps I'm spinning hard on the street but now I'm down to 16 mpg but it runs tooooo good to lean it out..... The 4.0 runs great when you give some fuel but it is a gas hog... Next up is the unichip so I can adjust the ignition timing and have multiple maps.....

Much harder to work on Toyota then motorcycles, with bikes you just get a pipe and a power commander and go....

https://www.magnaflow.com/02product/shopexd.asp?zone=main&id=10405
old thread about my exhaust.....
https://www.tacomaworld.com/threads/mangnaflow-6-x-18-round-muffler.331394/