Hi Suzanne,
First, lemme clear a misconception and that is I have a Suburban. I just cross-post here a good bit because the 'Burb forum isn't as busy as this Tahoe forum. Sorry for the confusion. That said, I don't have any wiggling issues with the longer wheelbase - one of the 'Burb's advantages when it comes to towing. I've (unwillingly) pulled as fast as 80 and no wiggling issues. We're using a Husky WD hitch with the 800 - 1200 lb bars.
Now about the bags and tongue weight. It's bit of a mystery to me as well:
1) I'm measuring 400 lbs of tongue weight with a Sherline scale that fits under the ball of the trailer's hitch. The factory spec for my trailer is 300 lbs. Best I can surmise, that's supposed to be wet - meaning 40 lbs of propane and an Interstate Group 24 battery. I've upgraded to 30 lb LP tanks, which added about 60 lbs (10 lbs per tank of gas, plus the 20 lbs more that each tank weighs) and I've added another 120+ lbs with a Stromberg-Carlsson rack over the LP tanks which holds two 5 gallon Jerry cans full of gasoline. Plus what I store in the trailer's front storage compartment. I'd think the Sherline would be showing 475 - 500 lbs, so the double axles are obviously picking up some of that load.
2) Assuming the 400 lbs is a correct measurement of hitch weight, and there's another 100-ish pounds of hitch and sway bars to add, we're looking at 500 - 525 lbs on the rear of the truck, which is rated for 800 lbs. And I've got 1250 lb rear springs - an upgrade from the factory 1000 lb springs that came with the air-ride suspension. It still squatted with the WD hitch pulled up tight enough I worried about it breaking. The ball is set for the correct height so that the trailer leans forward just enough to prevent sway that can be caused by the trailer leaning backwards. Of course, there's another 10 gallons of fresh water we carry in the back along with luggage, fishing gear, tools, and recovery gear, so that contributes some more weight. Finally, there's also the possibility that the factory specs for the Winnie's hitch weight are so much BS.
Hence the Air-Lift bags. My longtime mechanic and I installed them. It's not overly complicated - you could do it at home but I just don't care to crawl around on the driveway that much anymore. You basically squish the empty bag up between a couple of the lower coils and keep feeding it through until it's all inside the spring. Not as easy as it sounds - the plastic is pretty stiff. Other than that, the most difficult thing we encountered was ensuring clearance for the air lines beween the top of the bags and the spring perches. I also found out you can't always judge the spec sheet. After a conversation with Air-Lift, we measured the free length and the inside diameter of the springs before ordering the bags. Indeed, they were not the Z-71 spec bags but the nice thing about Air-Lift is they make a lot of different sizes so you can get very close to a perfect fit.
Since we got them installed, everything has squared up nicely. I run 10 lbs normally around town and then 40 with the trailer. I might try 45 on this next camping trip just to see. But it's a huge improvement.
Bob