That’s what I’m surmising as well. Perhaps OP wasn’t clear in their description above, but the bleeder screw MUST be located at the TOP of the caliper, and pointing UP. It’s often physically possible for a diy’er to install a right-side caliper on the left, or visa versa. When that unfortunate event happens, the bleed screw will be at the bottom of the caliper and point down. It’s impossible to bleed the caliper in that configuration. If that’s what happened, OP may rest assured they are not alone. The forum search feature (link above left, this page) will expose a bevy of posts on that very topic.
Photos of the calipers as installed would answer a lot of questions.
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While showing the bleeder screw position… lol
Just curious, I wonder why the folks who design brake calipers don’t make it nearly impossible to install them on the wrong side, upside down?
That would require useing common sense that seems to be in very low quanities these days. 
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You’d think that the engineering design review process would discover & correct that problem. Years ago I had a design review for a product subassembly I was designing, and the reviewing engineers immediately spotted a connector problem. I had spec’d a connector configuration with protruding pins, pins could have been easily damaged when subassembly was sitting on the shelf waiting to be used. That’s why technical folks ask others to review their ideas before releasing them to production.
The same casting is used for both sides, the machining for the bleeder screw is the difference.
When installed on the correct side (left), the bleeder screw is at the highest position.
These brake calipers were engineered and manufactured in your day.
That’s not it; the caliper is properly installed. The orientation of the bleeder and the hose is with the bleeder at the top of the caliper. That said, the mystery remains.
Those things can be like mirror images, easily mixed up. And of course, it is possible to get an incorrect part.
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Have you tried the rubber brake hose clamping method to isolate the problem hydraulic circuit? I’m guessing the problem is either the booster, MC, or the ABS unit. Presuming your brakes worked well prior to the new caliper, the ABS seems the most likely culprit. If problem is MC or booster, that would have to be a remarkable coincidence. You kept the fluid level in the MC maintained through-out the caliper installation process, right? One other thought, when you did the manual bleeding, did you press the brake pedal all the way to the floor? If so, that will sometimes damage the MC internal seals, b/c the piston moves to area it doesn’t normally visit, and those areas can develop deposits over time which will damage the seals.
Did you perchance happen to let the Master Cylinder run dry? If you did that, then the MC has to be removed and bleed on a bench, in a vice. There is a bleed kit and a procedure for that. You cannot bleed the MC on the vehicle.
No dispute, best if done on bench, before installing; but I’ve successfully bled my Ford truck’s installed MC by slightly opening each output line (one at a time) while an assistant presses on the brake pedal, then closing the connection before raising the pedal, similar to using a bleed screw. Gets the air out, but makes a bit of a mess. Not sure how well this method would work with a brake booster configuration.
Good point that if MC ran dry during any of the procedures, the MC must now be bled, one way or another.
Diy’er problems with bleeding brakes, very frustrating. Not fun. OP’s backup plan is to hire a shop to do the job for them, using the shop’s pressure bleeder gadget , and if necessary, the shop’s pro-level scan tool to exercise the ABS valves.
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We kept the jug of brake fluid handy throughout.
SInce the brakes seem a bit improved, I’m wondering if we did over-extend the piston in the MC or dislodge some debris and it has settled back into the bore. Probably wishful thinking but my sone says the brakes are better
Because they often use the same caliper bracket on both sides
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I’ve noticed the same thing after a brake job, for some reason the pedal seems to slightly firm up over the course of a couple of weeks all by itself. I’ve attributed that to air remaining in the hydraulic fluid working its way out with brake use, w/time bubbles rise up and out through the MC’s vented lid.
Stopping performance seems to improve a little also, but I think that’s a different effect. My guess, he pads/shoes bed-in and more precisely match the surface of the rotors/drums over time.
Thanks! Maybe I’m not crazy or stupid. It has been a frustrating week of brake problems. The one that started this thread was my son’s. In the middle of it all my grandson’s 08 Impala stopped stopping. Turned out to be a brake booster failure. I picked him up to loan him a vehicle and when we got back to our place, we smelled hot brakes. The L. rear hub was 517 degrees! New caliper. Enough!
Diy’ers often find brake work frustrating. Seems simple enough conceptually, but in truth brakes are very exacting and unforgiving. And there’s a lot of fiddly-bits to contend with. Pro’s develop a sort of muscle memory to handle the fiddly bits, and have the correct tools and have done the job many times before so know what’s important what isn’t, so overall brake work is much easier for them. Diy’ers who enjoy a challenge, a puzzle, however often actually enjoy brake work. How enjoyable it is depends a lot on how quickly you have to get it done.
Thanks. Well and wisely stated. Being able to work on something without pressure of having to get it back up and running in short order can, and usually does, take enjoyment out of the project. And certainly, having the correct tools is a factor. The older I get the less I enjoy crawling under the car. . .