I'm not a big fan of bilsteins.
IMO, a high dollar shock is not worthwhile until you are running the truck hard enough to feel the shocks fade. With most of the wheeling here, I haven't experienced that. If you get there, pony up for a good bypass shock.
Poly Performance has a pretty good shock for a reasonable price, might look into that.
If the front is fine, then leave it. You can run very different shocks between the front and rear, as they are very different systems with different weight loads.
But for the rear, I wouldn't run the billy's again.
Baby Beast 2- 1999 4Runner SR5
Baby Beast -1987 4Runner SR5-Gone, but not forgotten