Higher grade fuel is just a temporary fix to the problem, and shouldnt be used exclusively. Filling it up with premium is just a way to diagnose which problem it is, so if it goes away, that tells you it is in fact spark knock and not something else. These trucks are made to run on regular, so when you go back to that fuel, and the rattle comes back, then the issue is still there. Seafoam will cure it, other things like changing spark plugs, wires coil pack, and pcv valve will also help. You can clean your maf sensor, iac, and throtle body as well. My 4.0 does this from time to time, i just dont let it bog down when going up hills and its not a problem. Just curious, did you run the seafoam through the fuel or into the brake booster??
2004 4x4, ex-fleet vehicle. 4.0 v6 with 110 k, 4.10 gears.
Modifications: Whelan hidden strobes, Ion 174 alloys, yokohama geolander at 235s, billet grille, airbox mod, Dynomax exhaust. slight torsion crank. More to come!!