Ever since I've put new 100# valve springs in my 130K mile old 5.7L it seems like I can't keep the valves adjusted. Could it be time to replace the factory lifters? This is my first experience with hyd. roller lifters and I don't know what their expected lifespan is.

 

I doubt there's anything wrong with the lifters.

What kind of rockers do you have? If they're the stock rubber ones, their tips may be wearing out. Also, the lock feature of your rocker nuts may have worn out, and they might just be backing off.

Try some new rocker nuts, or even just add some jam nuts to the ones you have. Look closely at the tips of the rockers where they run on the valve stems.

 

And while you're in there, take a close look at the root of the rocker studs. If you see a nice clean, shiny ring around the bottom of the studs, they may be pulling out from the extra force of the new springs.

As for the roller lifters, determining the lifespan is a complicated equation, involving engine temperature, valve acceleration rates, valve spring rates, peak RPM, and lubrication type. If you're using a clean, fully synthetic lubricant, the typical life is 350,000 miles. If you're using top-quality mineral oil, the life may be 150,000 miles. If you're not changin oil regularly, the bottom falls out of the equation and the life may be unpredictably low.

 

I'm starting to think it could be the nuts not holding "torque". I can get ARP ploy locks but I don't know if those would clear the stock valve covers. If not, which poly locks will?

This engine has been well maintained with (mostly) dyno-juice. When I had the rockers off to change the springs I didn't notice any stud pulling, when I change to poly locks (or new nuts), I'll check the studs again.