Handling

No different. It may ride a little smoother.

Gas Mileage

17 -21 MPG depending on driving conditions.

Power

Much better. This is the way it should be.. The exhaust has a nice sound and the truck has ample power. GM should have done this. I don't think that it has switched out of over drive once when climbing a hill or mountain. On dry pavement it is no problem breaking the rear wheels loose. On wet pavement in 4 high it is sometimes possible to break all 4 loose.. They 4.3 could never even come close to doing that.

Driveablility

Much better. You can tell that the 350 is a better balanced motor than the 4.3 . All around it seems much smoother. It is especially noticeable in the smoothness of the idle.