1991 Chevy Silverado

I have a 1991 Chevy truck the factory motor blew and I got a Goodwrench 290 hp crate 350 I put it in and set the timing to top dead center with the computer unhooked and when I hooked back up it advanced the timing to about 14 degrees once it worms up it ackes like its out of time. I put the timing light on it and like I said at idle is about 14 degrees advance when I rev it up to about 2500 rpm it jumps to about 40 degrees advance and it runs like crap if you can help it would be great thanks so much if you need more info let me know.