Well i just swapped the gears i am running 4.6 diffs original cog was 19 teeth with the factory ti mags 265 75 16 tyres and the speedo was spot on.
With the 35's i tried the other gear i had here wich was 17 teeth couldn't believe my luck the speedo is spot on again at 50 and 60 k's so far need a freeway run at 110 yet .
Easy swap takes just a few minutes.