KA-T ballin’ outta control!!
Lolz.
your cat might be plugged a little, that could explain your gas mileage and wierd smells after beating on it, the cat would be getting very hot at that point,i have an s14 with 274231km on it and i drive 100km a day and i get over 700k to a tank and thats running 91, if i run reg i might see 550-600k to a tank
if its not running right, pull the ecu out and check the codes.