Thinking very seriously about selling my Tradewinds 40' DP and going back to an Ex to tow a trailer with. My last Ex was an '01 4wd early 7.3L and I added a 4 inch turbo back exhaust and muffler, a DP 60 and 80 horse tuner and an A&E injtake. I would like to get another PSD, but DW isn't too happy with a diesel and I need to know what to look for in a V10 as far as mileage and engine condition.

 

The V-10 is a pretty durable gas engine and they seem to go 250K miles with very little concerns with just good basic maintenance and care. If I was shopping for a replacement gas EX I would be on the hunt for one with less than 150K miles (the less the better).
You will want to look at the exhaust manifold studs/nuts and expect to see a few missing as these modular motors tend to suffer broken exhaust manifold studs to some degree by 100K miles. Shop fees for stud replacement should start around $800 to do them all, so factor that into the negotiations. It a job that can be DIY by a owner with tools and patience, I had 2 broken studs when I installed my headers.
The early motors (up through '02) only had 3 or 4 threads for the spark plugs, as a result there is a greater chance of a plug blowout if they aren't torqued snugly. The later motors have more threads (like 7 I think) and the plug blowouts aren't really an issue with these motors, but running a little higher torque than spec is still considered prudent. I have mine at 28/30 ft/lbs vs factory spec of 17.
As this will be bought to be a tow rig consider looking for wagons equipped with the better 4.30 gears vs the more common 3.73s, the deeper gears will deliver a better towing experience, you will also want to look into some tunes from 5Star as the improved shift strategy is worth the price to me when towing heavy. If your plans call for larger than stock tires (more than 285/75R16) and you will be towing 7,500lbs+ then you should be looking to regear it to get to an effective 4.30-ish gear ratio to keep your towing performance in the sweet spot. These gasses don't have the torque of a PSD so gears play a very big and important role in setting them up to be good tow rigs.

Our V-10 EX is our dedicated tow rig for our 12K TT, we have logged over 47K heavy towing miles with this gas powered wagon and with our setup it handles the work pretty well, I have zero regrets with my choice of gas over diesel 11 years ago. Our only hiccup along the way has been a fuel pump failure at a local campground, otherwise it's been smooth sailing.
Our EX is sitting at 135K miles with a 4" lift, 35"s, 4.88 gears, Banks headers, 3030XL muffler and 5Star tunes. We use a Hensley Arrow WD sway elimination hitch to keep the 41' long, 12' 2" high 12K lbs TT properly behaved behind us. It gets 7/8 MPG towing on country roads with small towns and lots of stop and go, 8/9 MPG on highway towing trips with 3 trips over 400 miles at 9.5 MPG, my best yet. Unloaded with the cruise set at 65 MPH it still gets 14.5 MPG on the highway, just 1 MPG lower than its best ever run when still all stock.
Good luck!

 

313k miles on my 02 V10 with a lot of towing of our 28' TT. Only thing slowing it down is the rust....Minnesota salt!