Those appear to be caster shims. One appears to be marked 4 De(g). And also marked No-Sl(ip), which they obviously aren't. The shims should go between the bottom of the springs and the top of the axle pad. Original ones (at least the ones I found on my truck) had a depression for the center bolt on top and a nub on the bottom that fits into where the center bolt would go if there were no shims.
Yes, you need to replace them with probably the same taper (4 degrees.) The thick part should go toward the rear of the truck. If you get it aligned afterward, they may want to replace the shims with a different taper if your caster is out of spec. Spec for a 1/2 ton is 1-3/4 degrees +/-1/2 degree (that's measured at the kingpin, and isn't necessarily the same as the shim taper.)
