I have a '91 Corolla wagon with a 3-speed automatic transmission with 149,000 miles. Bought it at 110,000. Runs great. But, lately, about 6 weeks after the latest fulid change, it now upshifts late when cold. When first started up, it won't upshift at all. Upshifts fine when all warmed up. The warmer it gets, the closer to the proper rpm it will upshift. My tranny service firm has changed the fluid twice now since I've had it - they've been around a long time and seem to know their stuff. They suspect worn rubber valve components. I've thought about draining the fluid and installing Toyota-brand fluid, but am just guessing. Or, vacuum problems. Or, just wear, but these things seem to go more that 149K without trouble, often. Any ideas would sure be appreciated. Great site, first post!

hm check your tranny filter
Good luck