Do not use Transcend - it's a waste of money. I have been very happy with Napa hydraulic/trans oil. It carries dex III, GL, C4 and other important ratings. It is cost effective, professional and comes in 5 gal pails, so that works for the flushes and fills from just 1 pail. Napa also sells the external and internal filters as well.
For the best bang for the.buck, you are absolutely correct. However, all reports that I have seen from all of those who have done this, the Transyn does significantly lower the operating temp of the trans. That said, most Allison dealers will do their best to.dissuade you from going with converting to Transyn from regular motor oil as it is very difficult to get ALL of the motor oil.out of the torque converter, and the Transyn is NOT compatible, not.even a.little.bit, with the.motor oil. Which has shown to.cause problems.
My father switched from Dextron to Transyn in his Monico 40' RV several years ago, and saw a 30+ deg F reduction in trans temp in normal use. It also extended the service interval to at least 50k miles. He never had any negative.issues with this. Positive only. He convinced me to go with the Transyn on my newly factory remanfactured trans for my A3. Time will.tell. At least, I will have the Allison factory 2 year parts and labor warranty, if it was not one of my better decisions. I do trust my father's advice. It is absolutely amazing how smart he is the older.that I.get. Funny how that works out...
The Allison remanfactured 1541P came with Transyn already in it, which helped.make my decision.