Ummm, yes...you DO have to load the suspension to install the Metcos.
I love the ease of installation of the metcos, but if I were to do it again, I'd do longbars. The metcos have grease zerks that are almost impossible to access, and are much more finiky compared to long bars. You have to tune the metcos. Long bars typically are just bolt on and go. Much more user friendly in the end...and who cares if you have to unibit your frame to install them. That's easy.
When installing metcos you're supposed to get the brackets on, bolt the bars into place in one of the brackets...have your jackstands under the frame...then when the bars are in one of the brackets (think I bolted them into the front first), then load the suspension, then put the bar into the rear bracket...and in order to do this you're going to have to adjust the threaded portion of the bar. If you adjusted them while the truck was on the ground and the bar was fully bolted in, they're probably wrong.