You listed a 3 speed transmission. Is that correct? The A604 is a 4 speed.
I use a 1988 Grand Caravan with the 3 speed transmission to pull an enclosed trailer that's bigger than the van and have never had a problem. I have two minivans with the 4 speed. That transmission would explode before I got to the end of the driveway! The wrong fluid in the 3 speed transmission will cause a shudder for a second or two during torque converter lockup. It can be duplicated for verification by holding the gas pedal steady above 45 mph, then tapping the brake pedal. That will make it unlock and lock back up in a couple of seconds. If you feel a shudder every time it locks up, suspect the wrong fluid.