To our little world.
You trailing arm can be found under any 1/2 ton or 3/4 ton, they are the same. Take a look in the local wrecking yards. They sometimes come up on the parts board here but mostly as pairs and shipping is expensive unless you find some close to you. As far as your tranny, hey it's a truck! not a sports car. Final tranny ratio is always 1:1 unless you go with a newer 5 speed or 4sp auto. Hit the search feature and you will find info here on Gear Vendors and overdrives.
Most likely you have a Eaton rear which only came in 4:10 & 4:56. Upgrading to a newer rear like a 14B FF with higher gears would help the top end. It just depends on your tire size and how fast you want to go. A rear end swap would be chaeper than a OD unit.
Now lets see some pics of you baby
