If I go with a 185amp Alternator from DC Power will I need to upgrade my wire that connects to output post?

 

Well at that amperage you should.
If you have #4 copper the max length
should not be more than 6' and your
also going to want to put a fuse in
the line because that cable will hold
up long enough to start a nice big fire.

If you want to look at a sizing calculator try this one
Wire Size Calculator | GTSparkplugs

Sean

 

What size cable is on the truck stock? Is that cable big enough for a 185 amp alternator?

 

If you ask me, no...

It's some dinky wiring that seems to be just enough to keep the truck running within spec.

This is 2/0 wiring that I installed last weekend: Super Start® 04357 - Battery Cable | O'Reilly Auto Parts

It's designed for a 7.3, but can be made to work with a 6.0.

-The wire that goes down to the starter is already 2/0, so you're better off NOT replacing the cable all the way down to the starter. Simply cut the existing cable and new cable, use a butt connector to connect them, then cover with shrink wrap.

-The harness .5 to 1 inch too short to reach the driver side battery. You'll need a small piece of 2/0 wire, 2 butt connectors to splice, and some shrink wrap, but it'll reach.

That's all I really had to do to make it work and it's much better than having to make your own cable.