I have a 04 Lariat Scab RWD with the 6.5 bed on it, so it is a long truck. It has 163k on it. About a month ago I decided I would do a suspension refurbish on it (among other refurb items) so I replaced the OEM rear shocks with Monroe reflex shocks & replaced the front coil over shocks With Monroe quick struts. When I finished, I took it to get a front end alignment and the alignment guy told me they didn't do the alignment because the lower ball joints were bad. I paid them the inspection fee of $21 and took it home. I replaced the lower ball joints, upper control arms which include the upper ball joints, and the inner and outer tie rods with Moog problem solver servicable parts. Everything except one of the outer tie rod ends were bad. I took it back and they did the front end alignment and it rides much better. However, the fact remains that between 53 and 56 mph ther is a slight shimmy that has always been there. Also, the bed wiggle when hitting a bump is the same as it was when I bought it new 10 years ago. I have always run my 18" tires at 35 psi (door sticker) and it is the best that it will do[ridewise].

Just my observations.

 

My 05 seems to be getting worse over bumps as well. I have 161k+ on it.