You need a glycol test of the ATF because those cars are known to leak antifreeze into the transmission cooler circuit. The resultant glycol contamination will give the symptoms you describe. Replacement of the trans and torque converter is the fix. If the glycol test is negative then the shift adaptations need to be erased to see if the symptoms go away. If it does then it is a problem in the trans control module and there is an updated module that addresses this problem.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff