From what I've seen, all the slides, regardless of how far they extend, use the same length tube assembly, and the specs show 70" long. From the Lippert site, units made prior to October 2013 use the 18 tooth gear packs, so the slide tube needs to be-
Lippert 334648 Inboard Inner Arm Tube Assembly For 18 Tooth Gear - 2.5" x 2.5"
When I replaced the forward tube on my door side large slide due to broken teeth on the tube, I used the tube for the 15 tooth gear pack which has four teeth per inch and just used a 15 tooth gear instead of an 18 tooth gear. For some reason, the part of the tube where it bolts to the slide bracket is too long compared to the original tube, so I had to cut off part of the tube and drill a new hole so the gear rack was the same distance from the slide bracket, otherwise I would have run out of gear rack before the slide was fully retracted. I have not seen where the new rigs that use the 15 tooth gear packs have the gear packs mounted, but they may be inboard of the frame instead of outboard. I purchased the new tube from
https://www.rvupgradestore.com and it was much cheaper than ordering from Lippert, but was drop shipped directly from Lippert.
Lippert 143710 Inner Slide Out Arm Inboard 2.5 x 2.5 Tubing, this is the 15 tooth tube.
What is the problem that you are needing a new tube?