Too many variables and there's no rule book on this anyways. Your truck/situation will be different. Bottom line, drive it and enjoy it until it "needs" them. Don't try to outthink them and change them anyways or just because. Get your money's worth out of these first.
Similar story...tons of guys on here with lower ball joints going out at all variables of mileage (30-50k) with lift kits on my body truck. Well, 109,913 today and still running the original lower ball joints. Everything else on the front end has gone bad and been replaced, but by lowers are holding strong. And I'm not going to replace them until they go. FWIW, my original uppers made it about 25-30k after the lift install before they went out. Everything else (tie rod ends, etc) made to 100,000.
'02 F150 XLT 4X4 SCrew. 5.4L
K&N FIPK/Amsoil Filter
Flowmaster 40 si/do Exhaust
305/70 16 GY MTR Kevlar
16X10 MB Motorsport wheels
Rancho 4" lift
Rancho 9000XL Pro Series Resi Shocks
FireStone Air Bags
Autometer Carbon Fiber Oil/Trans Temp Gauges
Carbon Fiber Interior (www.dash-kit.com
Peterson Fluid Sys. Remote Oil Filter
Troyer Performance Electric Fans
Amsoil Fluids Throughout