If I got this right, an operator needs the latest (as of Nov. 12) Cab3 upgrade to run the Triplex using 4-digit addressing; however, with the 990 (CabII) the engine will run fine so long as an operator uses 2-digit addressing.
In Sean's case however, the latest Cab3 (as of Nov. 12) upgrade did not fix the issue of engines running out of sync using 4-digit addressing, but it does work using 2-digit addressing, yet Dave Olson suspects hardware problem and recommends sending it back in.
I cringe at this thought: are the odds favorable that there's a hardware issue with every single triplex and therefore a total recall would be prudent and ethical? While it's anecdotal, the only method I can think of to prove otherwise is if someone reports successful out of the box (meaning not sent back to Lionel) operation using 4 digit addressing via the latest Cab3 (as of Nov. 12) update. Thus far, no review that I've read as reported this success. I honestly hope someone can prove me wrong.