Rusty,
What issues would arise, if any, from using any one of the new ATF's in any Automatic Transmission. The Mercon LV & ATF +4 appear to be mineral based while the Dexron VI is synthetic based. All three of them have dramatically increased shear resistance and friction modifiers to prevent clutch shudder which should benefit all of us?.
Billy T

I use Dexron VI in the P/S-Hydroboost system, and Dexron III in the tranny. Since the tranny temps stay very cool, I have the Mag-HyTec pan (extra 4 qts. and cooling fins), and I change ATF every 50K, the tranny rebuilder said there's no reason to use D-VI.

I'm not familiar with Allisons, but I'd put nothing in there not specifically approved by Allison. For those with the Allison 542, I'd go with synthetic because of its somewhat higher resistance to heat. The 545 with the larger capacity should do well on mineral oil-based.

For Ford trannies (like the older C6), I'd continue to use Type F (Ford M2C33) as long as available - and the same for the P/S; that's what I use in my '87 Ford van. Type F is becoming harder to find, so the choice is straight Mercon (not the Dexron/Mercon labelled).

BTW, the main difference between Type A/B (Dexron) and Type F is the slip-stick differential (SSD). SSD indicates whether friction increases or decreases as two sliding surfaces approach lockup. GM transmissions were designed for smooth clutch engagement, so friction decreased as the mating surfaces approached lockup. Ford trannies' were designed for firm lockup, so friction increased as engagement was approached.

Friction modifiers are what create the SSD, and can be formulated to reduce shudder. However ATF isn't a panacea for shudder, so if that's an issue with a tranny, it could be symptomatic of another problem.

As far as "shear-stable" claims, I suspect this is marketing hype, since it applies primarily to the viscosity index improvers (VII) use in multigrade motor oil. I guess there would be some merit in a "multi-grade" transmission fluid, but the initial use of multigrades was to improve cold-weather engine cranking. Properly refined base stocks (in the viscosity range of ATF) are by nature shear-stable.

Regarding shudder, I sometimes feel a chatter or shutter at about 30-40 when pedaling hard like leaving a light going uphill. I always wondered about it but it never seemed to get worse and went away as soon as I lifted to normal throttle. I check the tranny fluid regularly, it's always nice and clean looking and smelling. Should I get it serviced anyway?

Allisons need to use Transynd if you are going to synthetic. A little spendy the first time because they need to flush the tranny, but overall very cost effective as it extends the service interval by 3-5 times. It also tends to shift a little smoother and run a little cooler.

Danny, the shudder should be felt only when the tranny is shifting - if it's transmission-related. There's a possibility that the filter is plugged causing the pump to cavitate, but my guess is that it's engine-related.

Edit: The symptom could also be that of a bad clutch

SM, most likely the lower temps are a result of the flush and filter change, not the synthetic fluid. There is no difference in cooling properties between synthetic and mineral oil.