upgraded steering to 08.5 pitman problem 98.5 though...
 

I have a 98.5 duelly 4x4. I bought the proper pitman arm that seems to be listed everywhere for the steering rod set, but it is too larger for the stock steering box spline. Like maybe a few washers? to press it right against the rod but it still rocks at its maximum tighteness without a nut or anything... is there another pitman arm for this steering that is about 2mm smaller or stock for this year?

If you actually have the 08 Pittman arm, all the washers in the world aren't going to help you, the 94-99 trucks have a different taper on the joints.

Get the right Pittman arm if you want to be safe.

Thinking ream
 

Would love to find correct pitman, but images on Google of hd 99 steering isn't helping to figure pitman requirement.

At this point I'm thinking ream the stock pitman, anyone know reamer bit required? Google isn't winning that battle either. :(

The best thing to do is to get the correct 98/99 linkage. They were the same T type steering and all the joints will have the correct taper.

Basically the upgrade is to run 98/99 style on the 94-97's and the late 3rd gen stuff on the 2000 up trucks.