sounds like a vac leak or (but you had it for a while and it's unlikely) you did not replace the Idle Air control Valve and housing - look at the housing, does it say 2.5 or 4.0?
check the rubber elbow that's on the line going from the valve cover to the intake manifold under the t/b, sometimes that cracks and would leak vacuum which would cause high idle. Check other fittings on the manifold as well to see if there are any of them with a problem, could also be one that goes to the dash climate control or the one that goes to the t-case for front axle disconnect - you can remove them off the fittings on the manifold and put your finger on top of the fitting to see if the idle goes down (except for the MAP one, that needs to be plugged). Other thing i can think of is if the throttle lever on the t/b is not going all the way back down (maybe the cable gets stuck) so try to push it back down by hand and see if that's helping.
