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How long does this occur each time? If it is for just one or two seconds, lightly tap the brake pedal while holding the accelerator pedal steady. If the shudder stops, then occurs again a couple of seconds later, that is the torque converter locking up. The most common cause of that is the transmission has the wrong type of fluid in it or an additive has become depleted. The lock-up clutch is grabbing too aggressively. It should be allowed to slip a little, and engage gradually.

This torque converter shudder can last much longer too, but the clue will still be it stops when the brake pedal is pressed. Also, this is not felt in the steering wheel.

If the steering wheel is vibrating, it is more likely a part is loose or worn in the steering or suspension systems. Have it inspected at a tire and alignment shop. The people there are experts at finding the causes of noises, vibrations, and bad tire wear.

A worn universal joint can shake the entire truck. That vibration will be about six times faster than wheel speed. You may also hear a loud metallic clink when shifting between "reverse" and "drive".

Yes, if your transmission specifies a particular fluid. This problem occurs most commonly when the transmission is serviced, as in a maintenance fluid and filter change, and the wrong fluid is put in.

I forgot to include some of the other clues. The first one is the speed you observed. Twenty five mph is a little low, but possible. Lock-up typically occurs beginning around thirty five mph, and only when the engine is warmed up. On a cold winter day, I have to drive about four miles before it locks up. At higher speeds, like fifty five mph, there is no shudder, but I can feel the engine slow down, and the tachometer drops 200 rpm. On a hot summer day, it is already locking up within the first mile. I get that shudder too but it is real bad when I cruise at a steady forty mph. Does not occur at any other speed. Mine is a 1994 Grand Voyager, and I know from the previous owner, they changed the filter and put the wrong fluid in. This is a real common annoyance with an easy fix.

Sounds like it was attacked by an incompetent do-it-yourselfer. That is what happens when you do not come to 2CarPros first!

I am in the middle of Wisconsin, and I really hate cold and snow!