1992 auto transmission problem

Step on the gas and the transmission doesn't seem to want to downshift smoothly. It "vibrates" as if the transmission is rapidly shifting back and
forth between gears before finally engaging the lower gear. Happens more during loading conditions, sometimes finally downshifting other times not. Been doing this since 40,000 miles but getting worse now. Has anyone heard of this? I'm sure the shop will just tell me time for a new transmission. : ( Any thoughts?
jer
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lvjetboy via CarKB.com wrote:

Likely suspects are pressure regulation problem, crud in the valve body passageways (the jitter between gears or servo chatter) or slippage. The 'during loading' makes me think excess slippage. First, some slippage is normal--makes for smooth. Cadillac's have more, trucks have less and Corvette's have it just right! Excess slippage may cause the transmission to switch into the 'git home' mode, raising servo pressure upward to produce a 'hard shift.'
Do the low-cost and easiest thing first. Change the fluid and replace the filter. If there's any improvement, repeat both in a couple of hundred miles. If symptoms of slippage continue, get it adjusted soon before you cook some parts. Above all, don't let just any transmission guy swap out the transmission--there are dozens of THM versions that will "fit." Get to a Corvette specialist--stay with something that shifts smoothly, performs well and will handle the torque. PJ
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Thanks for the ideas PJ. I didn't know slippage could cause that strong vibration I'm feeling in between gears. I start with the oil and filter. Wish I knew a good vette mechanic in Vegas :( I've always had dealer gm mechanics work on it, but they don't seem very good and not nearly worth what they charge.
jer
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lvjetboy via CarKB.com wrote:

Check here: << http://www.vegasvettes.com/
PJ
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Thanks for the LV vette link PJ. I checked that forum, not much going on... but I'll give it a shot. Driving to work yesterday I was thinking...slippage? As in a clutch? Is automatic transmission slippage caused by excessive "clutch" clearance or other facters and if so wouldn't that slippage also occur with a manual downshift? With manual downshift I get immediate response. No vibration, etc. Same also from a stop. If I floor it in 1st gear then manually shift to second, then manually shift to third...etc...I get no slip. Yet if I'm cruisin' in drive or overdrive up an incline at say 50 or 60 or 70 mph, then give more throttle w/o manually downshifting? The transmission sometimes vibrates before automatically downshifting.
Has anyone else experienced this? Is there a tech bulletin? Like I posted, this has happened to me since the transmission (and engine) had 40,000 miles on it. Not much. 40k is not enough for normal wear and tear to start acting like this.
It's almost like the transmission is rapidly switching from high to low quickly and causing a vibration before finally deciding to go to the lower gear.
jer
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