my 93 with a 318 is better on MPG than my 94 with a 3.9/ but I have never had one 9 MPG-bad. except my 88 D 100,318, 1st year they had TBI.
My 94 (3.9 auto reg cab short bed 3.55s) got a best ever of 18-once- usually 17 on a solid highway run, 14 in the winter in mixed driving, my 318 one (club cab, converted to 5 speed by me, also 3.55s) gets 20 on the highway and 17-18 in mixed driving. never did worse than 15, even towing, with this one. both trucks 2wd,
my 90 (3.9 pre magnum long bed also 2wd, 3.55s) got 16 in town/20 highway, like clockwork.