Yes, more info would be helpful. By the way, Fred from Rogue Performance ("Fredness") is THE expert on 3.0's.
Could be something with the MAF depending on the year. 1998's have a limp mode that might help you diagnose it. Unplug the MAF and see if it runs better. If it does, chances are you need a new MAF. My daughter's 98 was like that and I ended up replacing the MAF on hers.