Won't crank after installing new fuel sending unit.

[Mels72C20]

Okay guys, I finally got the correct fuel sending unit for my truck and popped it in. Key on, 1/2 a tank, yeah it works. Then I proceeded to change the tranny fluid, new pan, gasket, and dipstick to fix the really bad leak I had. Filled it to just below the add mark and went to crank it up to start getting the level right. Truck fired up momentarily and cut off. Now it won't crank at all. First of all, I am carburetor stupid! Any help on what to check would be appreciated. Truck has a 350 with the original Rochester quadrajet.