93 PA transmission question

[aavp96]

93 PA with 145k miles

About 6 weeks ago my transmission started shifting hard.
It shifted with a thump, typically between 1500 and 2000 rpm.
Three weks ago I took the pan off, changed the filter.
The fluid was dark brown.
I found a half moon shaped white plastic part in the pan also.
I refilled with Dexron III.
The hard shift improved for a day, and came back.
In the last few days the car not just thumps but shakes during up or down shift between 1500 and 2000 rpm.

Any suggestions?
Is this a sign that I will need to invest in a new transmission?
If yes what is the typical cost to replace a transmission on a PA?

Thanks

[Jrs3800]

That plastic piece you found is a chunk of thrust washer, not really common but it does happen from time to time with these 4T60-E's...

I am going to tell you to check the Vacuum Modulator on the front of the transmission( looks like a small gray coffee can on the front of the trans with a vac line attached to it... And thats if it hasn't been replaced )... If there is any trans fluid coming out of the Vac end of the Modulator then its shot and needs to be replaced... As well check the vac line to the modulator... If there is a vac leak, or the Modulator is bad it can cause a harsh shift

[aavp96]

Thanks
I will check the vacuume modulator
It looks like they sell between $15 to $38 at Advanced

[HotZ28]

Be sure to check the trans mount (left front, drivers side) while you are at it. Best way to check the mounts, is by looking for excessive engine movement while the trans is in drive @ 1500 rpm & brake applied.

[aavp96]

Thanks for the help.
I have picked up a vacuum modulator from Autozone. $12.99 +tax. AZ Filters brand. MV303
It was really easy to remove the old one. It had fluid inside.
The only watch out is that the original vac hose is too short for it.
I had to cut a 4-5" long piece to make it work.
During the 5 miles test drive it seems to be working well. However it does jerk a bit when I put it in to gear the very first time. (Drive or reverse.) The modulator is adjustable, so I will try a few settings in this weekend to see if I can make that better.
Thank again