Lost power the other day, feels like limp mode. I felt it happen, and seems like I may have heard a faint pop from under the hood. P0299 popped up, she starts and idles fine, and very initial acceleration is okay, but then no power. Turbo was rebuilt a few years ago, pretty new. What is the procedure to check vacuum lines/solenoid? I sucked on the line going directly to actuator diaphragm and it seemed to move (motor off), but I don’t know how to check the solenoid, etc, or if thats the best route…

Have you checked your intercooler hoses for splits, or to see if one has popped off at the end? They usually split at the bottom where you can't see it.

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05CRD: GDE Hot ECU & TCM tunes, Provent, Cat filter, Facet lift pump, TransGo kit, Florida TC, Samcos, stainless brake lines, HDS thermostat, Renegade light bar,
RL super sliders, Bilstein adjustables, Al's Gen 4.5 Arms, 235/85-16 Duratracs, DTT rear, Elocker front, EVIC+TPMS, Turbo timer, McNally pillar gauges, Weeks Stage II kit.

You have a blown intercooler line. Most times it's the one between turbo and intercooler as the heat deteriorates them faster.

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GDE FT Ecotune, EHM, Weeks kit stage 1 & 2, Carter 4600 lift pump, Upgraded tranny, Fishing boat hauler!
New at 164K: head gasket, rockers, exhaust valves, ARP head studs, Injectors, 5v Bosch glow plugs, water pump, timing everything, serpentine everything,
New at 225k: new head, timing belt

I got similar situation some years back in one of my trips to Florida. In addition to, lost of power I got heavy black smoke. A crack of about 3/4 inch at the underside of the inner-cooler hose between the cooler and the intake manifold close to the cooler end. Some "duck tape" gave me a temporary solution while waiting for the shipment of the replacement hoses from ID parts at my brother's house (2 days).

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Sergio05CRD