To the O.P. jimd40
If you ever get around to installing a rear trac bar, be sure to replace "AT THE SAME TIME" the stock rear stabilizer bar with a heavy duty version. On my 2007 E350 chassis, they needed to be installed together for I believe they shared mounting points or something like that.
It seems people who do one or some, but not all the upgrades typically mentioned for the suspension, later learn that under "other" conditions, what they have done so far has proven to be inadequate. If you later realize you still have a handling problem, consider the full deal, some of which you have already addressed.
- heavy duty front & rear stabilizer bars
- heavy duty shocks
- heavy duty front steering stabilizer
- rear trac bar
- wheel alignment done with the rig loaded ready for a trip.
And as always, make sure your tire pressure is correct for your particular load.