^ Agree with redwood here. Remember some folks have a bit of a pessimistic view on things or just don't know better. I'd give my 10 year old "mostly stock" pickup a good chance of pulling 6-8 percent grades plus with most any TT on the hitch without slowing down if the curves didn't dictate. I know it'll rip 5th gear at 60-65 mph uphill with a boat anchor on the hook and do the same at 75 mph in 6th. My issue is egts, as I have a pretty crude tuner that likes to pour the fuel to a stock turbo that doesn't clear out the lungs as good as it could making that kind of power. Actually better than a good chance, I do it semi regularly. That's the benefit of having the better part of 1000ft lbs on tap.
To the OP, sounds like your sub/Tahoe did well. Don't believe the guy with the 5.4. It isn't the raw powerhouse he's making it out to be.
Yes a 7.3 cherry excursion woild really do the trick, but like you said, they're not getting any less gold plated every day. You can make marked improvements in towing power with several of the new SUVs, but for the price you pay for them you could buy a HD diesel tow pig of your favorite flavor. Crew cab, topper with a carpet kit and it's like a sub without the 3rd row seats!
