Looking for help with troubleshooting strategy on 4L80e swap into 1500 Yukon XL.

Issue after install is: Whine at front of trans, maybe from TC(?), varies with RPM, and only in gear (FWD & REV). P/N is quiet. Trans appears to shift solidly into gear, wheels move when elevated but will not move vehicle on own power.
Background:
- New, stock-style converter - installed per spec, 1.03" to mounting pads, shimmed to flex plate barely over 1/8" final gap
- Trans is unknown quantity supposedly rebuilt
- I took off pan, to install HD2, clean, no apparent issues, filter confirmed installed
- Pump removed and inspected, looked good/new - no grooves on gears or housing
- Dip stick "full" reference check/confirmed with pan removed
- Trans filled with approx 14 quarts
- New cooler lines - Tru-Cool cooler flushed (no debris), blown out and new trans fluid circulated and drained.
- 4L80e wring modification, PCM segment swapped including diagnostics
- P1810 code observed once, cleared and never came back
- Trans cable appears to be adjusted and operating correctly
Plan:
Will be able to get line pressure readings in next two days, so...
- If line pressure is low, remove trans and start with?
- If line pressure is within spec?