Agree with what Larry just said - raised steering arm is better than dropped pitman arm. (If for no other reason than it keeps the stuff up higher away from rocks.)
Also agree with what cyclic said - good bloody luck finding one with less than 4" of rise.
Also agree with what Larry said - height sensing proportioning valve is the likely culprit.
"Bump steer" means it will turn itself when you hit a bump and the suspension compresses. If you go over a speed bump a little too fast - does it try to rip the wheel out of your hand? If it doesn't, and it's only doing it under braking, then it's not bump steer.
Dropped pitman arm is a compromise used when the suspension lift is so high that the raised steering arm is not enough. That adjustable "connector rod" between the pitman arm and the steering arm is a "drag link". There are also offset drag links. If you want a 12" lift, you might end up needing all three.
For a 2.5" lift you really shouldn't need anything, which is why they don't make 2" raised steering arms - don't need 'em.
If you go to the Skyjacker site and look up lift kits, they show 3 2.5" kits for that truck. Two of the three say that the dropped pitman arm (part #CA50) is required (and I ask - if it's required...then why isn't it included?), but the third kit does not say the dropped pitman arm is required.
I don't see the dropped pitman arm as a problem with the truck in the OP - 1/2 ton, not running 40" tires, doesn't have a 6" lift, probably doesn't have a big block or other 700 lb. engine. It's mild, not wild. Broken steering box output shaft is a very rare failure. With those Chevys it's much more common to just rip the steering box off the frame - which is why they make support brackets and weld-in frame reinforcment/repair plates for those trucks.
I wouldn't do the dropped pitman arm until after I determined if it's the proportioning valve.
I can't recall offhand - do those trucks have the normal proportioning valve (usually right under the master cylinder somewhere) AND the height-sensing valve back over the rear axle? If so, then yea, I'd bypass the extra valve. I think that valve is primarily intended for trailer towing anyway, if there is a lot of tongue weight.
If not, then I'd get rid of the height-sensing valve after I installed a normal proportioning valve.