I've been told by Firestone complete that struts are blown.
Heather at Boulder bars said to check my pocket before I ordered new struts with 70k on them.
Does sound like they are shot?

Did I just buy struts at almost $400 for a simple fix or are they truly blown?

Not to be overly pedantic but the KJ does not have a true "strut" in the front end rather it has a coil over shock assembly in a conventional front suspension as distinct from a MacPherson strut. As such if the shock absorber part of the assembly has gone bad than it can simply be replaced although I'd advise you have a shop do the swap of the shock(s) as compressing springs for shock replacement is rather hazardous.

With your lift I'm not sure what spring/shock parts you are using.

Setting the above aside I would not think a "blown" shock in a coil over assembly would cause rattling and would wonder if something in the front suspension is simply loose.

PS have you tried the "bounce" test of the shock. Last time a "tire" shop told me my shocks were gone based on leaking fluid I asked for some of the fluid on a paper towel and compared it to the rain outdoors; you can guess the answer.

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Sold to LOST member my 05 Ltd, GDE Stg II turbo + TCM tune, SunCoast TC w. Transgo kit, Steiger window regulators, Samcos, Fumoto valve, 2nd gen filter head with Lub. Spec. bleeder, Hayden clutch & 11 blade fan, inverted spare, P-1 battery, BF Goodrich Long Trail TAs, Etecno1 glow plugs, timing belt at 50K miles/8 yrs