Check the wiring on the cap. Pay close attention to cylinders 1 & 3:

 

I did mine on my 2003 blazer 4.3 liter l/s and I found a video on u tube listed as lower intake gasket replacement made the job so easy
GM 4.3 Vortec lower intake manifold gasket ... - YouTube just enter this into your address bar and am sure you will enjoy the help I did.

 

OMFG Captain hook i love you, I'm a dumb ***. 1 and 3 were mixed. i apparently remembered that the first time i put it back together, but not this time, lol. i marked them before i pulled them, but i forgot those two were flipped. But now that i switched those two it wont start at all. would that now be an issue of the distributor being off a tooth? I'm going to search some crank no start threads for now, but if you got any ideas give a shout out here please.

 

Did the same exact thing with mine when I did the lower intake I crossed one wire and that,s all it was.Just do a google search for wiring order 4.3 liter Chevy.And with any luck that,s all that,s wrong with yours.Wire to the same image as your motor they show the round cap then they show the one with three wires each side with the coil on the passenger side of the cap.That,s how my 4.3 liter was Good Luck.

 

Distributor could be off. Better re-check it