1998 E350 5.4L 4R100 Transmission Code P1754 - Rough Idle, Squeal from Bell Housing

I own a 1998 Ford E350 with a 5.4L V8 and 4R100 transmission, currently at approximately 276,000 miles. When I purchased the van, it was reported to have only a blown engine, but that issue has been resolved. I replaced the engine with a salvaged 2000 5.4L V8 from a donor vehicle. After driving about 20 miles, the vehicle began running roughly and emits a noticeable squeak or whine coming from the bell housing area. The idle is stable, but there are two diagnostic codes: P0500 (which I believe indicates a faulty vehicle speed sensor) and P1754. The transmission appears to be dragging the engine, causing shaking under load. I have already replaced the solenoid pack and inspected the coast clutch valve—both showed no issues. Upon visual inspection of the transmission internals, it appeared to have been recently serviced. The overdrive light on the shifter now functions properly, which was not the case before. After performing a lift test following the solenoid replacement, no codes were detected. However, when I perform a KOEO (Key Off Engine On) check, the P175-4 code appears and remains persistent in memory. I have removed the transmission control module from the 2000 donor vehicle and am unsure whether this might introduce new issues or provide any benefit. Any insights or troubleshooting steps would be greatly appreciated.