Transmission problems
 

Looking for some ideas on what to check. I know very little about the inner workings of automatic transmissions. I have an 84 which is lacking power and has a shutter while driving coming from rear of vehicle. Engine runs smooth but I feel like the car is towing a trailer. It seems to shift just fine, fluid is at proper level. Upon chasing this problem by doing things that could be hit or miss, I changed the fluid and filter, as well as the vacuum modulator. The fluid I changed out did not appear abnormal or burnt. It also lugs the engine while making turns from a stop.
Any suggestions that can help me get started would be appreciated. If it gets too costly, I will just replace it with a good used one.

Replacing the fluid has always fixed those kind of problems for me. You've already changed your fluid, so I'd say your tranny is probably shot.

I'm not an expert, though.

Sounds like a problem with the differential.

And I'm not an expert either.

All that stuff sounds "weird", not like any failure I am familiar with.

Did you properly check the level, engine running etc?

How is the vacuum line and bowden cable?

Before you get much deeper I would have a 928 expert look at it.

My '83 kind of feels strange when it accelerates cold. It warms up and drives fine. It kinda feels like a torque converter problem.

I did correctly check the fluid level. I will admit that I havent yet checked for good vacuum to the modulator yet. Also, when the car has been sitting for a while cold, it almost feels like im starting off in third gear just to illustrate the engine lugging.
After driving a couple hundred feet, it starts to smooth out but the problem described earlier is still there. I am using dextron 2. Not sure if thats the correct fluid or if it would even make a difference.

That sentence is what is making me think differential. Ever try to drive an ATV w/o a differential on pavement and try make any sort of sharp turn?

Why not jack the car up and check rear wheels by hand.

If you had a vacuum problem, you'd feel hard, abrupt shifting, not really loss of performance, .......save for the effect a vacuum leak has on air/fuel control.

Before you do anything else, I'd replace the fluid yet again with a quality synthetic, like from Amsoil.

I'm running Castrol ATF, and I don't like it. Also, I had no good way to flush out the old fluid from the cooler and lines, so I have a mix of old with new/cheap fluid. But I did drain the torque converter.

I know what you mean. My Euro (3 speed) in Reverse felt that way, like it was dragging something. Doesn't matter now since I toasted it the other day.