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The 4L80E and TH400 are vastly different transmission, one is electronically shifted, while the other is not. You need to put the exact tranny in that truck that it was designed for. The reason it keeps blowing fuses and dies after a few seconds is because the PCM realizes that there is no transmission, and shuts the truck off. PCM means Powertrain Control Module, meaning, it controls the engine and transmission, it has to have both to work properly.

I believe the TH400 is mechanically shifted(pressures and the whatnot dictate when it shifts), which is why alot of guys don't like em, and the 4L series are all electronically shifter.
 

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The 92-95(me thinks) chevy C/K series used PCM(Powertrain Control Module) controlled engines, they don't have a ECM. The PCM controls both the engine and transmission, mainly the shift points, and the TCC.

The 93's are very very similar to my 94, I know them like the back of my hand, and the transmission has a huge effect on the way the truck runs, if there's nothing sending signal back to the PCM, even though it's OBD1, it'll recognize it and stop operating properly. You have to have the connections hooked up, all of them.
 
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