2006 Grayhawk Ford e450 v-10: Power increase

I have a 1995 454 TBI eng in a 15,000 lb Class A and have done the following to improve performance. I measured performance by 40-60 mph times. When I first bought the MH it took 22 secs to go from 40 -60 mph. A tune up, plugs wires distributor cap brought it down to 19 secs. Headers, FF mufflers and CAI reduced it to 14 secs. Headers would add about 80 HP to the older 454's and 460's the newer V-10's will probably be less. Check on the Banks web site for your year eng and type for HP increase. Advanced timing from 4 degrees BTDC(stock) to 9 degrees BTDC further reduced time to 12 secs. Also transmission no longer downshifts at the slightest hill and engine temps were reduced only rarely the fan clutch come on any more except on very steep hills out west. My stock engine only produced 230 HP, the mods brought it up to a little over 300 hp. Nothing increased the MPG except installing a Vacuum gauge and watching it. 8.5 mpgs went to 8.7 mpgs if I use it when traveling. If you don't know what your baseline performance is before any mods you won't know what the increase will be and it is hard to tell just by noise or "seat of the pants dyno". So before spending a lot of money be careful when asking your friends about their mods if the just tell you it sounds or feels like better performance.