[ElKotze]

The cheapest way would probably be to swap your rear gears, but I'm almost sure you have to change your carrier to a series3 . Series3 posi carriers are about $450, get a ring and pinion (308, for example) for $200 and I would also recommend a master overhaul kit for $200, comes with new bearings and different shims. That's exactly what I did, now I'm cruising 70 mph @ 2600 rpm. Your 454 won't have any trouble pushing whatever gear you want to put in.