You need to check each port individualy of the 3/2 valves to insure they hold/release vac as they should, especialy holding.

On the OP valve, pull vac on it with a gauge and watch to see if it bleeds down past where it's suposed to be.

If all really does check out(it's a minor miricle), then your vac sugnature needs adjusting. Closed throttle you should have way high vacuum, I forget the figure(this is what the 3/2 valves do) to keep downshifts from being felt, just the slightest throttle and it should let the vac valve on the IP take over, and go by it's setting.

On a trans with lots of miles, it's like that article said, OEM new specs are not always going to cut it. Adjust, fiddle, play, learn. If it's not flairing of slipping, it can be made to shift well usually.

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K