Box could be worn or the tie rods are done. I did my steering box in about 3 hours including replacing all the hoses from the pump to the hydro boost to the box to the cooler to the pump. Cross your fingers and hope that the lines when you take them off pivot. I paid like 230 for the box (there are 2, a 32 and a 36 spline it think) and maybe another 120 for all the lines to replumb it (mine had both nuts rusted to the hardlines and I couldn't get them off without replacing them) Shop would of done it for 600 + cost of hoses.
Tie rods I just always take everything off in 1 shot and get everything new 1 time from AutoZone, then its lifetime warrantied and I stick them for all the parts the next time too. Pop out the pitman end, off both of the steering knuckles, and drag it out. Then just measure from grease joint to joint to make each piece as close as it was before. Always get an alignment after doing rod ends. Parts were like 250 + alignment for my dually 350 front end, shop wanted 650 + alignment.
How to tell where the issue is? Jack up the front of the truck on both sides, go to the tire and grab it 9 and 3 and wiggle back and forth while watching the pitman arm, is the arm moving more than just a little, there shouldn't be much slack in the box for that arm to move, if it moves that's not good. if instead it stays firm but you can get movement out of the wiggles in the steering rods, then you got bad tie rods. Grab the each tire at 12 and 6 as long as your here and check for movement in that plane, if so you got a bad ball joint. 965 at the dealer + extra for parts discovered in the disassembly. I did the entire front end for that (Mile Marker hubs, hub bearings, rotors, pads, seals, shaft u-joints, and of course, the ball joints)