Yep, there's tons of info on here about what's the best plug to run in the 4.0's. After reading just about every thread out there pertaining to them, I bit on the Autolite APP985's and wow, what a difference! New plugs had to be re gapped due to the knucle head at the parts store throwing them around on the counter (I had to ask him to be careful eventually). As I pulled an old plug and replaced it, I checked the gapping on the old ones too. Not a single plug was less than .065!!! Can't believe she would even crank. It's yet another testament to how tough these 4.0's are. Immediate improvement in idle, throttle response and, dare I say, she's got a little more pep to her now. For $4.56/per, I'd say it was great Sunday afternoon project/investment.