What Brendan said is true.
If you want to load it like a 1 ton, then when changing to a smaller number rear (like a 4.10) you won't be able to get your load moving (as well).
The 4.10 is available from people who part out(I got one recently) as is the 4.56. I've never seen a 3.90 available. I've heard of a 3.38 but think it is a myth. Havn't seen one myself... only read about people who's second cousin talked to a guy who saw one at a swap meet 10 years ago.
Consider looking on Pirate 4x4 or other such boards. There might be someone who would LOVE to swap you a 4.10 for your 5.14. The 5.14 is RARE, and wheelers and boggers love that tough old Eaton axle and the 5.14 is the holy grail of gears for that axle.
If you just want to go faster, and still want to load it up like a 1 ton, consider buying one of those Spicer auxilliary transmissions that are in the for sale board... or some other aftermarket auxilliary tranny.
I have 19.5" tires. That helps things go faster.
