Ok guys a few weeks ago I bought a 93 camaro 3.4l (automatic), it sat up for around 6 months and it has 243xxx miles on it. Now the issues I'm having is I can't drive the car in Drive (D), it acts as though it's slipping and makes my car shake, the trans does shift kind of hard when I go into Reverse or OD but not terribly hard, it just does a slight lurch no clunking or anything. Reverse works fine, 1st worked fine last time I tried it (the day I bought it) I've never actually tried 2nd, but Overdrive also works fine, no slipping or shaking or anything like when it's in Drive (D), but if I'm in OD on the highway usually doing around 45-60 mph and hit a steep inline or hill and the car tries to ease itself out of overdrive back to 4th it makes a loud god awful grinding/scraping noise but only at the initial shift and only if it's switching back to 4th at low throttle, if I give it enough throttle to make it shift instantly back to 4th or even 3rd it doesn't make the noise only when it's trying to "ease" itself out of Overdrive, I included a sound clip of the noise it makes, if anyone knows anything about the problems I'm having or that grinding noise please me know.
Btw my fluid IS due for a change but it's not low or anything, I checked that first, thanks in advance!

 

It sound to me like clutches are slipping. There is not al lot of meat on factory clutches so most likely the fix is a rebuild unless this a low miles trans. As for the exact problem, You trans has already out lived the estimated life. All it assuming it did just wear out anything that would cause a drop in hydraulic pressure will cause the clutches to slip but once they slip like that getting them to stop slipping is very rare. Most transmissions that are rebuilt are never really diagnosed. They just rebuild them and check everything.