I installed ls3 430 hp with a 4l65e crate engine and trans. This is supposed to be plug and play, but I don't think so. When I let off the gas going downhill, I get a lot of loud rumble from the exhaust. Is this something that can be fixed by taking it to a tuner. Thanks Bob

The Throttle Cracker and Throttle Follower settings can contribute to a lot of noise under deceleration, but in my case I thought of the noise as popping rather than rumble. But the sound might depend on the exhaust system.

So, maybe.

Thank You, Bob

Yes, a tuner can fix that. The rumble is from the engine deceleration fuel cut-off being too aggressive for your new cam. They can adjust the tune to smooth that out. It's a common issue with these swaps.