...how about solenoids etc. Nobody have that scan tool in Bulgaria...
IF you could find a scan tool that could datalog the shift, that would truly help. I'd have to dig back in the manuals but there is a way to tell when the shift command is electronically given and you can monitor rpms, VSS and OSS to determine when it shifts relative to the command as well as torque converter slippage and lockup. Lacking that we have to rely on logic and intuitiveness to ascertain the cause of the problem.
Shift solenoids rarely fail and if they do it usually just will not shift, so that would be far down the list of potential suspects in my mind. I have personally witnessed strange shifting due to a faulty TPS however. And I suppose if there was a fault with the VSS/OSS that could cause a problem in shifting as well. What is odd to me is the fact that it appears to only influence the 1-2 shift and not the other shifts. Ford diagnostics involve a lot of special tools and specific procedures not readily available to the layman but I like to refer to the troubleshooting charts to help pinpoint the path forward.
When it comes to the automatic transmission, it becomes even more involved as we are now adding hydraulics to the customary electrical and mechanical issues to diagnose. Shift concerns span all three; electrical, hydraulic and mechanical. When it comes to improper shifts or no shifts, we start with the electrical aspect of the Powertrain Control System.
The electrical components responsible for input/output controls of the powertrain control system include the electrical harnesses, the PCM, shift solenoids, EPC solenoid, TFT sensor, OSS, TPS and MLPS. Ford's testing process involves testing of these components with special tools and pinpoint tests.
The hydraulic/mechanical concerns span from fluid level (as well as condition), 1-2 shift accumulator, line pressure, stuck solenoids, stuck valves and blocked or damaged solenoid valve screens (in the valve body).
This all gets even more specific when addressing the 1-2 shift (only). Electrical: harnesses, PCM, shift solenoids and OSS. (Note TPS omitted). Hydraulic/Mechanical: damaged/misadjusted MLPS, intermediate clutch pressure, line pressure, 1-2 shift valve, 1-2 accumulator valve, shift solenoid malfunction(SSA/SS1), gasket damage(valve body), number 8 ball not seating, hydraulic pump (damage, cross leaks, porosity, balls missing), intermediate clutch assembly (seals, piston or friction components), intermediate one-way clutch (not holding or damaged) and finally the planetary one-way clutch (not holding or damaged).
I find it interesting that the TPS was omitted in the diagnosis of the 1-2 shift but I found that to be the case for each specific shift, 2-3 and 3-4. I conclude that if the TPS was at fault it would interfere with ALL the shifts and not just a specific shift.
If you have followed along this far, maybe you see something I see as well.
If it were me, I'd be asking what did "I" change that could have possibly caused this? You mentioned replacing all the sensors... I'm wondering if there could be some issue with the OSS? Is it the correct one? Is it faulty (even though it is new - it happens)? Is there an issue with the harness connector?
It may be worth giving the OSS another look. Maybe even backtrace and replace the new OSS with the old one?
Easy enough and worth a shot?