I have a friend that replaced his TBI 350 motor with a GM crate Vortec motor (rated somewhere around 255 HP vs. 210 HP on the stock motor). All he did was put on the adaptor intake (Vortec heads to TBI), and he has shorty headers on it. Absolutely no other modifications to the TBI or ECU on the truck.
He had the truck for several years with the stock motor and it ran good, but the Vortec crate motor was noticably more powerful. I'm sure with a few minor ECU and throttle body tweaks it would have been even better.
Basically he had a dependable smooth running crate motor under warranty that was noticably stronger than stock.