Any auto experts on the forum?

Something strange has been happening my 1992 Merc 190e 2.6 auto for the last few months.

It started with a slighted delayed shift out of 1st (as in it requires less load and more RPM than usual to shift from 1st to 2nd). As it progressed it would shift above 2500rpm from 1st to 2nd even if there's very little load, and it would only briefly stay in second before going into 3rd.

Now it will hold 1st gear to 3000rpm no matter how low the load is, and if there's moderate to heavy load, it won't shift until it's 4k if not more, and shift directly into 3rd. . It does this while cold or warm, though it seems to be very slightly better when it's hot.

While the car is cold, as I'm accelerating in 1st gear in D, if I shift into N and then back into D, it will shift into 2nd gear like it should, and not hold the 1st gear. When it's fully warmed up, and when i do this, it will just shift into 3rd at a lower rpm.

Also while it's warm, and I accelerate moderately, it will kickdown to 1st when it should shift into 2nd.

This is a mechanically (vacuum, shift cable, and kickdown switch) controlled transmission.

Any ideas what this could be caused by? Fluid looks fine and hasn't changed level. the vac line to the vacuum modulator is good (only changes shift stiffness and not point anyhow).

Something internal like a particular piston?



All other gears seem to shift just normally fine. (2 to 3 when it can manage to get into 2, 3 to 4)

Thanks for your help in advance!