Shifting issue
 

I have a2006 ram 2500 with 6 speed manual. I have an issue when it get about 80 degrees outside shifting into rev or the 2 lower gears is very difficult and sometimes can only be do by turning of engine put it in gear and starting. Clutch has been done and then done again still happen. Slave cylinder has been replaced. I can't recall ever having issue in winter. Anyone have any thoughts on this?

What type of fluid are you using 90W120 or royal purple synthetic?
Sounds like the synchronizers are worn out. They are brass and have a clutch material on the inner facing cone arrangement and tend to wear out.
try a fluid change and pray.

So I'm guessing those are inside the tranny. Can they be replaced?

Shifting issue
 

Yes they are inside and each gear has a synchronizer. You will need to get another exchange transmission unless you are a wiz at mechanical things. Some special tools are required also.

before you do that did you get a new hydraulic set up? NOT A STOCK UNIT! You have to get the aftermarket one it has more rod travel! I just went thru this and know exactly what your talking about!

They are pricey but worth it! http://www.ebay.com/itm/SouthBend-Clutch-Hydraulics-Dodge-Cummins-Diesel-03-12-NV5600-G56-6spd-HYDX-750-/151685472955?hash=item235128a2bb&vxp=mtr

I replaced it with a new one that was, I'm assuming stock because it didn't change anything. You had the issue when it was hot that it would not shift into rev or 2 without pumping the clutch or shutting off motor? It is more pronounced when pulling a load.

Is it the rob on the slave cylinder or the rod to master cylinder?

Yes same issue! Get one and be done with the problem! Trust me you'll be very happy! Follow the instructions on rod set up to the letter!

Ordered will keep you posted