Bad milege and broken seat

[Green machine]

I have a 1999 4x4 supercab with a 114,000 miles.
Recently I have replaced the Alternator, plugs, wires, air filter, and pully tensioner. I have run Amsoil in it since about 40,000. It runs smooth and strong but it my milege seems crappy still. The only thing left in my eyes could be the fuel filter. Other thoughts would be the cat or some type of air/fuel sensor, but my thinking would be that it would not run good.

Help!!!

Forgot about seat.
Two back support rods (about 2mm Dia.) have come loose at bottom of seat and poked through back cloth on seat. Looks like the weld broke.

Anyone know if you can remove seat cover to get to rods to re-weld?

Thanks