I love the 30 Valve V10. I averaged 6.8 MPG over a 450 mile stretch the other day and I can change the oil for about $25.
6.8 may not sound good, but I tow a 4000 lb Saturn and I was running hills and passes from the Grand Canyon into New Mexico with a full fresh water tank. I typically average about 70MPH when conditions are right, but on that run I hit snow, dust storms, dust / rain mix, rain, sleet, more snow, high winds... well you get the idea... So I'm guessing my average speed was between 65 and 70 to get 6.8MPG.
I just have to watch when my wife drives.. She is more aggressive and will keep it wound up to 75MPH so I need to watch the mile markers and stop for gas a little sooner. I'll take a nap and wake up looking out the passenger window at a semi driver wondering how a stupid V10 with an automatic is passing him going up hill.
Also I swear by the transmission brake on the V10. It's a little wonder. I can take 4% grades fully loaded with hardly a tap on the hydraulic brakes. My startup checklist includes tow/haul ON. 100% of the time. Wish I could reprogram the computer to turn it on for me.
Only mod I've made to the engine is a Bank's air intake kit, which just opens up the air flow into the engine. Once the computer adjusted, mileage went back to normal, but I have more power at lower RPMs and the engine has a much deeper sound, versus the high pitched whine. The engine sounds much nicer at wide open throttle and I got some super cool Banks RAM-AIR decals!