Originally Posted by pblue
My 2013 and 2012 toyota minivans weigh about 500 pounds less than my PM 2500 high roof (empty), but don't have the huge rpm increase when dropping from 6th to 5th gear at highway speed. My Promaster feels like an additional load is on the engine right before it jumps to 5th.
Why the difference?
Different transmission. Understand that the 62TE (transverse 6-speed automatic) that Chrysler has been using for a number of years (including in the PM) is a glorified 4-speed automatic with an additional underdrive unit. Theoretically there are 8 combinations (1 low, 1 high, 2 low, 2 high etc) but two of them work out identical (I believe 4th i.e. overdrive in the main box plus underdrive in the secondary box is identical to 3rd i.e. direct in the main box plus direct in the secondary box) and two of them are so close that the transmission does not shift through both of them, so there are only 6 useful speeds.
This is also why the shift from 2nd to 3rd sometimes feels awkward ... It is really the main box shifting from 1st to 2nd together with the underdrive box shifting from direct to underdrive. There is a lot going on in that particular shift. And 2nd ("1st direct") and 3rd ("2nd underdrive") gears are awkwardly close together ...
What all this means is that they are stuck with the same difference between direct and overdrive that the old 4-speed box had ... Transmissions "designed for the purpose" always have the higher gears spaced closer together. This one is stuck with an inconveniently large gap between its single overdrive gear and direct.
It also means that it has to unlock the torque converter for a moment during the shift to avoid having a large jolt ... that's why the revs go up momentarily just before the 5-6 shift.
I recently had a current Chrysler 200 as a rental, which has the ZF 9-speed. The upper ratios are all close together, which means it can do a better job of picking the right one, and the steps between them are small so it need not unlock the torque converter. I know Chrysler took some flak for how these were calibrated early on, but they must have been working on it; I thought it was fine.