I have a couple V-10's, and like them. Plan on 8 to 9 MPG towing, and 11 around town.
The spark plug failure issue is common on both the earlier model V8 and V10 engines. I blew one on my 02 at 50K miles. Haven't had any issues at all on my 99, but it's only got 20K on it too. That one spark plug issue is the only money I've put into either of them.
As far as towing ability goes, it won't keep up with a powerstroke by any means, but they do ok. For example, my 99 V10 (motorhome) weighs in at 17,000 pounds. Then I add my Jeep and trailer behind that. The Soldiers Summit climb will knock me down to 35 MPH, but I can live with that.
On the truck, look for the 4.30 gear ratio. I tested both the 3.73 and the 4.30, and there's a huge difference between the two.