7100 lb-rated new Silverado towing 4000 pounds

I tow ~5000 lbs with a 1999 F150 V8 with lower specs than that newer 4.3 V6. It will certainly do it. WIth regards to fuel economy, it's still a heavy truck, the smaller engine will need to make the same amount of power than the larger engine, pull the same weight. It's not out of the question that they will be identical. What I don't know is what the more modern or efficient engine is...

8 speed auto would certainly seal the deal in favor of the v6