Weight and rolling resistance impact MPGs. Hence a mud terrain might get worse mpg than an AT even at the same weight. Those Falken AT3Ws look like a great tire but damn they’re heavy in C load 285s
I switched from stock rims with P265/70/17 Falken AT3W to TRD Pro rims with LT255/75/17 Cooper ST Maxx and went from 15.8 down to 13.9 avg mpg. Made me sad.