I only know of tow issues with the Ford V10.
1. It is a Gas engine :B My Cummins made me say that! :S
2. Some seem to have issues with the spark plug change, some report that it is difficult or costly.
So those that I have talked to that have them are very happy with their performance and pulling power.Many report good mileage empty and also pulling light. I would not consider 7 to 8 terrible for a strong gas motor. There are also many reports of these going an easy 250,000+.
Never had a V10, but did own two Ford 460ci power houses. The second was getting tired, and I replaced with a Ram,