Originally Posted by gkos_
So I changed the sparkplugs and it turned on beautifully but once I put it in drive and pressed the gas it had trouble going 15mph
Also it revs in park and in drive it doesn't.
Do you have COP or coil packs? If you have coil packs maybe you bumped the input to one of the two (or both) coil packs loose. On mine, the little retaining clips on the outside of the plug housing both broke when I changed them a few years ago... Check the coil packs according to the service manual witha multi meter, you may have a bad one. Also, verify that the boot are ALL ThE WAY seated on the plugs.
I had a '94 Explorer with a single coil pack for the 4.0, when the coil pack went bad, the engine would start and idle fine, and I could even rev the engine in neutral, but once I put a load on the engine I could BARELY go past 30 MPH.