tansmission problems

I have a '76 suburban been fixing it up. But a cupple of weeks ago i took it for a test drive and noticed it wasn't shifting in to 3rd gear.fyi engine 454 tranny 400 turbo)I had the trans rebuilt and still the same
problem persists i have spoke with a cupple of different people and different ideas have come up that maybe the the plunger in the carb was sticking or that the cam lobes were to far gone to build enough totque although it buils 5000 rpm's in park so i decided that, that was not the problem so i got under the the sub to see if ther was any loose parts that maybe i for got to install but the only thing i noticed this being my first 400 turbo is that it didn't have a shift kickdown cable like the 350 so again i asked around and some one told me that the small electrical prong on the trans on the driver side was called a shift kickdown selinoid that, that is what activated the shift so know that i have explained the problem and what i hope is the solution at least part of it is if the transmission shop rebuilt the trans and raplaced the kickdown selinoid then what i want to know is if the wire that plugs into the trans is a contant power feed or powerd by a relay and if it is a contant feed at what amperage so as i can run it direct from an ignition source

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