Starter engages when key is on

[Waco331]

So I have a 2003 Silverado single cab with a 4.3 and manual trans 

I purchased a running and driving 2000 Silverado with a 5.3 I cammed it had pcm tuned long tube and couple other misc. things drove the truck for about a month to ensure all working properly 

 

Performed the swap to install the 5.3 into my single cab the truck has sentimental value to me which is why I am swapping it 

 

swap everything over harness pcm motor 4l60 everything is bolted up plugged in. When I turn the key one click the starter engages and turns over by it self 

 

I have read forums and forums about this will not work and I have to go to a Dbw setup and I understand that, but there has been a couple I read where you could use a 2003-2005 express van harness and pcm or have the v6 pcm flashed to a v8 and it should work 

 

I would prefer for everything to work they way it was suppose to like factory so if I did a stand alone it wouldn’t work that way 

 

Maybe another option might be to just swap all electrical from the donor truck to the 2003 

 

I’ve lost countless hours of sleep trying to figure out which route to go and a direction 

 

and help would be much appreciated 

[Sharpz]

im curious.  What happens when you put the key to the start position and move past the on position?