This may seem a bit jumbled, but it's like my mind when I try to attack these problems...
The 5200 (if it's like mine) has two adjustments on the intake side (towards driver side)...one for idle and one for fuel...if you look on the other side of the carb there is another screw setting that I think is for air (I lost my diagrams and can't get back into the ARRC site for some reason) or maybe another fuel...but if you have that too far open your idle goes up (it's a slotted screw near the front of the carb).
Did you hook up the ICM connectors from the passenger side? Those are for idle control, but, apparently, they can be completely disconnected on the 5200...I'm still working on that myself...
Also, are you sure you don't have a vac line open somewhere? They can cause the idle to go up or down...plug up everything on the intake itself...there should be at least 5 outlets...depending on your intake...
Oh, and make sure the PCV cannister is connected under the intake and to the carb...
Did you hook up the EGR? (Dang, I think you just helped me figure mine out...I didn't hook that up yet and it usually lowers the idle...)