I've got a 2000 Expedition with a 4.6 and just over 100,000 miles. When driving at highway cruising speeds I get a vibration and a rumble sound as soon as I hit a slight incline. It just seems to happen when the throttle opens a little above the cruising level when encountering an increase in load. Other than that it runs pretty smooth. I have changed all 8 coils twice (don't trust the cheap ebay coils) and plugs with no change in the rumble. The engine seems to run great. It accelerates smoothly and free-revs like it should. I can't get it to vibrate while powerbraking, but I can get it to do it while driving in 3rd or 4th gear. I have also had the trans flushed. I had suspected the egr, but I'm getting no codes whatsoever. I looked in the throttle body and the egr ports look good from there. I have run seafoam in the tank and in the brake vacuum line. I have also checked fuel pressure and found it to be good. I changed the fuel filter anyway. I haven't checked fuel pressure when it happens at highway speeds, but maybe I'll try to see if I can do that. I'm thinking maybe IAC or TPS. Any thoughts? Thanks.