Knuckle Busters

Hi:
I hope this is posted to the correct forum. If not, please correct and notify me of where it should have been. I did search for this answer as well as where I should post it and this seemed like the right place.
Anyway...
I may include too much info here, but I'd want as much information as possible to make a decision, so I'm guessing you would too.
I'm re-manning a '97 4l60e (Z71, PWM edition) and am experiencing what seems like the overrun clutch engaging with 4th gear. 1, 2, and 3 engage nice but when 4th is commanded, it engages, but the engine seems to brake as well as it feels like a giant hand has taken hold of the tailgate and is pulling back on the truck. From what I've read, that appears to be the overrun clutch assembly engaging when it shouldn't. (as soon as it did this while test driving it, I neutralized it because I know the overrun frictions can be damaged very quickly when this happens). When it first went into the vehicle, I had a very similar issue. Before I could get back to the shop, it had lost 2nd and possibly 4th. It would run 1st up to about 4k RPM then shift directly to third and at about 50-60MPH, the TCC would lock, but I don't think 4th ever engaged again. While still installed I tested the band actuator by compressing the apply piston cup. It seemed to not have a bottom so I suspected that the anchor slipped. I opened her up and I replaced the band and the reverse input drum because it was lightly scored and the brand new band was toast. Test drive and I have the problem described. If I keep the selector in D3, the trans works fine through the upshift of 1, 2 and 3, and into the lockup. However, there did not seem to be any manual or commanded downshifts/engine brake until the vehicle was stopped. And of course, no usable 4th. Removed and pulled the entire thing apart down to a bare case again. Realized that I inadvertently compressed the incorrect input drum spring-pack above the apply piston. So I put the right one in. (used an aluminum piston spring on a stamped-steel piston. Opps) Also, the forward/overrun clutches seemed to have excessive clearance. However, none of the frictions were damaged and neither were any of the steels or pressure plates/wavy plate. But I scrapped all of them and repacked the set to specs. That should be adequate background info.
I've read how to bench test the input drum assembly and I'm stuck on the input sun gear. Somewhere I've read that when the 3/4 clutches are applied, the forward and overrun should remain free and the sun gear should overrun in one direction and lock in the other. But I've read this about the forward pack as well.
The bench test procedure was describe as such: "Apply air to the Forward Clutch feed hole on the Pump Cover, The Input Sun Gear should Overrun in 1 direction, & Lock in the other direction. Then apply air to the 3-4 Clutch. Again, The Input Sun gear should overrun in 1 direction, (The Forwards will "soft" apply....Non-Issue)."
I've been doing this for 30+ years and have never had to do a full test and have never had to test the movement/locking of the input sun. When I apply air to the forward clutch via the pump port, the sun gear locks solid. NO movement whatsoever. With the 3/4 activated via the pump port, the pack compresses and the sun can be spun in one direction, but not in the other. I have always considered that a passed test. Am I correct in thinking this way or should the sun overrun with the forwards engaged as well, such as the other thread stated? TBH, I have a difficult time understanding why the sun would be able to overrun the same way during both test operations. To me that would seem counterproductive. Also, since the overruns are activated by the same plate as the forwards, I can't fathom how the sprag wouldn't lock the forward sun in place. From what I can tell, the sprag spans both the forward frictions as well as the overrun frictions, so when that pack compresses, the sprag is effectively defeated which should prevent the sun from free-wheeling. Is that accurate.?
Thank you for taking the time to read this epic and offer advice.
Fred