e38/t42 4l80e swap not commanding 4th gear

Attachment 89951

Installed a 5.3/4l80e combo into an 87 rscb. ecm OS-12614088 tcm OS-24239927. Converted e38 to a custom 2 bar OS, Maf Failed open loop speed density only. T42 is a 2008 express van OS.

tcm will not command 4th gear. Wiring has been changed and triple checked, "U" brown wire moved to "S" location. Swapped ISS sensor wire on the tcu side from pin 45 to pin 26, added pigtail to vss and plugged in. 12v(pink) shows proper voltage. No codes are coming up and I cannot command 4th gear on VCM scanner.

With a stock 4l60e tune on the t42, trans will shift into 4th but throw a P2764 "Torque converter clutch pressure control solenoid control circuit low". then it will lock the converter and keep the trans in 4th gear permanently. If I remove DTC P2764 Transmission will shift 1-3 properly with proper lockup. This was all tested using the TCC lockup solenoid into pin "S" on trans to avoid premature lockup on the 4l60e tune. Relay was used to convert solenoid signal on the yellow/blk wire as I wanted to rule out tune issues.

Thanks for you help