I think it's time for 100,000 mile tune-up. Truck currently has 103,000 miles on it. I purchased my 2003 X almost 3 years ago with 68,000 miles on it. I had a former Ford dealership mechanic inspect the truck after purchase. He thought it was very clean. He thought the rear differential fluid had been recently replaced with a synthetic. At 75,000, I changed the tranny fluid and added Mobil 1 synthetic. All fluid was changed out with machine.

I noticed last fall that the truck would have a miss for a few miles after sitting in the rain. This weekend we took a 300 mile round trip with the truck and the miss never went away (it had rained the 3 previous days). For a while I was concerned that it may be the tranny, but when hearing the thumping at idle, I figured it must be a miss. Of the 30,000 miles I have put on the truck, half have been towing a 6,000 lb TT. Late last year we upgraded TT's and purchased one that weighs about 9,800 loaded. The X probably towed it 1,500 miles last year.

Should I change the tranny fluid, or should it be good for a few thousand more miles?

I plan on changing all the plugs and originally was going to use motorcraft. After reading Krewats post about the Bosch irridium plugs, I am considering them. What are the general thoughts on plugs?

Do I replace all the COP's or just try to find the bad ones (not sure if 100,000 if past life expectancy for these)? It seems to be the consensus to stay away from any COP's that are not Motorcraft.

Any other fluids that should be changed?

Thanks