2000 F150 XLT 4.6 V8 Automatic w/overdrive 642,000+ miles;
Last week while driving down a highway doing about 65 mph using the cruise control, my truck suddenly started running sluggish. As I described in the description, it also shifts between 2nd and 3rd very slowly and weakly. During the last couple of weeks I repaired several items that had thrown TDC's. One was the EGR system was clogged. I tore it down and cleaned the two ports out in the bottem of the throttle base plate. One was the speed sensor in which I replaced. One was the multi purpose switch (turn signal/windshield wiper etc.) which I rep[laced. The codes were cleared and have not returned. I suspected a clogged Catalytic Converter. I checked them all and replaced one weak one. Still the same performance issues.
Do any of you have any ideas as to what this could be?
Thank you!
Chuck

 

When I let it idle, it runs fine. When I start out driving very slowly it seems to run fine. If I try to gain speed quickly it starts to stumble at about 45 mph. The problem seems to be when I accelerate. By building up speed slowly it seems to do fine. When it hits about 55 mph, it goes into overdrive just fine. When I stomp down to downshift it stumbles. It seems as if the transmission is in between gears. I'm not ruling out the transmission but there is no slippage or delay at all when taking off from a standstill. While sitting in park, when I rev up the engine it starts sounding sluggish at about 3000 rpms.... This is sitting in park... Thats why I tend to think I have a motor performance problem. Any ideas?
Thanks again!